The World Health Organization (WHO) has recorded more than 100 attacks on health care facilities in Ukraine since the start of the Russian invasion on Feb. 24.

The "grim milestone" was crossed on Thursday, the organization said, adding that 73 people had been killed and 51 others injured.

Of a total of 103 attacks, 89 have impacted health facilities and 13 have impacted transport, including ambulances, according to the WHO.

"We are outraged that attacks on health care are continuing. Attacks on health care are a violation of international humanitarian law," said WHO chief Tedros Adhanom Ghebreyesus. "Peace is the only way forward. I again call on the Russian Federation to stop the war."

WHO representative in Ukraine Jarno Habicht said that across the country 1,000 health facilities are in proximity to conflict areas or in changed areas of control.

"Health workers throughout the country are risking their lives to serve those in need of medical services, and they, and their patients, must never be targeted," Habicht said.

WHO Regional Director for Europe Hans Henri P. Kluge, who visited a western city of Ukraine Thursday, said, "It’s a truly sad irony that we are recording this milestone of over 100 attacks on health in Ukraine on World Health Day."

"I have been personally struck by the resilience and fortitude of health care providers and indeed of the health system itself in Ukraine. WHO has been working to ensure supply lines remain open to allow lifesaving health and medical supplies to reach cities and towns nationwide, and continued attacks on health make this effort all the more challenging," Kluge said during a press briefing on Thursday.

According to the health organization, the impact of this violence is not only immediate in terms of the number of deaths and injuries but also long-term in terms of consequences for Ukraine's health care system. This is a serious blow to the country's efforts to implement health reforms and achieve universal health coverage, a goal toward which it had made significant progress before the outbreak of the war.

"Across Ukraine, 1,000 health facilities are in proximity to conflict areas or in changed areas of control," Habicht said.

WHO has been present in Ukraine since 1994, working to strengthen the country's health system, with a particular focus on primary health care and health financing.

Kluge said that "since 2015, and until Feb. 24 this year, the government of Ukraine has been in the process of reforming the entire health system, moving toward universal health coverage."

He added that Ukraine was making "excellent progress in turning the corner in the fight against tuberculosis (TB) and HIV."

"Ukraine was a beacon of best practice in Eastern Europe, with TB incidence falling by almost half in the past 15 years, thanks to the investment in modern diagnostic technologies to rapidly identify TB infection and effective treatment regimens for multidrug-resistant tuberculosis," Kluge said, pledging more assistance for Ukraine in order to rebuild the war-torn health system with local and national authorities.

"Health requires peace, well-being requires hope, and healing requires time. I speak on behalf of the entire WHO family when I say that it is my deepest wish that this war comes to an end swiftly without further loss of life. Tragically, this is not the reality," he concluded.

Ukrainian leaders predicted more gruesome discoveries would be made in reclaimed cities and towns after retreating Russian forces left behind crushed buildings, streets strewn with destroyed cars and mounting civilian casualties that drew condemnation across the globe.

President Volodymyr Zelenskyy said the horrors of Bucha, a town north of Kyiv where bodies of people killed at close range were found on streets and in basements, already had surfaced in a worse way in Borodianka, another settlement outside the capital.

"And what will happen when the world learns the whole truth about what the Russian troops did in Mariupol?" Zelenskyy said late Thursday, referring to the besieged southern port that has seen some of the greatest suffering since Russia invaded Ukraine. "There on every street is what the world saw in Bucha and other towns in the Kyiv region after the departure of the Russian troops. The same cruelty. The same terrible crimes."

After failing to take Kyiv, Russia shifted its focus to Donbass, a mostly Russian-speaking, industrial region in eastern Ukraine where Moscow-backed rebels have been fighting Ukrainian forces for eight years. Ukrainian officials warned residents this week to leave as soon as possible.

Ukrainian forces are in control of the entire northeast region of Sumy along the border with Russia, its governor said Friday, warning residents against returning while it was being cleared of mines.

"The area is free of orcs," Sumy regional governor Dmytro Zhyvytsky said on social media, referring to invading Russian troops. "The region is not safe. There are many areas that have been mined and are still not cleared," he said.

Zhyvytsky has said earlier that Russian troops were withdrawing from the area after Moscow's announcement of shifting its military aims to Donbass. Despite Friday's announcement that Ukraine forces were in control of Sumy, he said that the proliferation of unexploded ordnance meant the area was still unsafe for residents.

"If you hear explosions – and there have been many in recent days – it's emergency workers and technicians specialized in explosives. They are defusing the ammunition left by the Russian military on our land."

"Do not drive on the sides of roads and do not use forest roads. Do not approach destroyed equipment or orc sites! It's not time to clean up yet. First – demining" he added.

Sumy, a city with a pre-war population of around 250,000 people and the administrative center of the region, was besieged early in Russia's invasion.

In a sign of the intense fighting expected to come, Ukrainian authorities said a rocket strike Friday killed more than 30 people and wounded over 100 at a train station in Kramatorsk, a city in the eastern Donetsk region, that was being used to evacuate civilians.

Regional Governor Pavlo Kyrylenko said thousands of people were at the train station at the time of the strike, preparing to head to safer regions.

A Kremlin spokesperson acknowledged that Russia has suffered major troop casualities during its six-week military operation in Ukraine.

"Yes, we have significant losses of troops and it is a huge tragedy for us," Kremlin spokesperson Dmitry Peskov told Sky News.

Peskov also hinted the fighting might be over "in the foreseeable future," telling Sky that Russian troops were "doing their best to bring an end to that operation."

Spurred by reports that Russian forces committed atrocities in areas surrounding the capital, NATO nations agreed to increase their supply of arms after Ukraine's foreign minister pleaded for weapons from the alliance and other sympathetic countries to help face an expected offensive in the east.

Bucha Mayor Anatoliy Fedoruk said investigators found at least three sites of mass shootings of civilians committed during the Russian occupation. Most victims died from gunshots, not from shelling, he said, and some corpses with their hands tied were "dumped like firewood" into mass graves, including one at a children’s camp.

Fedoruk said 320 civilians were confirmed dead as of Wednesday, but he expected more as bodies continue to be found in the city that was home to 50,000 people. Only 3,700 remain, he said.

In his nightly address, Zelenskyy said Bucha's horrors may be only the beginning. In the northern city of Borodyanka, just 30 kilometers (20 miles) northwest of Bucha, he warned of even more casualties, saying "there it is much more horrible."

Ukrainian and several Western leaders have blamed the massacres on Moscow’s troops. The weekly magazine Der Spiegel reported Germany’s foreign intelligence agency intercepted radio messages among Russian soldiers discussing the killings of civilians. Russia has falsely claimed that the scenes in Bucha were staged.

On Thursday, a day after Russian forces began shelling their village in the southern Mykolaiv region, Sergei Dubovienko, 52, drove north in his small blue Lada with his wife and mother-in-law to Bashtanka, where they sought shelter in a church.

"They started destroying the houses and everything" in Pavlo-Marianovka, he said. "Then the tanks appeared from the forest. We thought that in the morning there would be shelling again, so I decided to leave."

Hundreds of people have fled villages in the Mykolaiv and Kherson regions that are either under attack or occupied by Russian forces.

Marina Morozova and her husband fled from Kherson, the first major city to fall to the Russians.

"They are waiting for a big battle. We saw shells that did not explode. It was horrifying," she said.

Morozova, 69, said only Russian television and radio were available. The Russians handed out humanitarian aid, she said, and filmed the distribution.

Anxious to keep moving away from Russian troops, the couple and others boarded a van that would take them west. Some will try to leave the country, while others will remain in quieter parts of Ukraine.

According to the Ukrainian government, 10 humanitarian corridors were operating on Friday to evacuate the civilian population from some of Ukraine's most embattled cities. From the city of Mariupol, which has been particularly hard hit by Russian attacks, a route for private vehicles will lead to the city of Zaporizhzhya, according to Deputy Prime Minister Iryna Vereshchuk.

From the city of Berdyansk, as well as from other places in the east, civilians will be picked up by buses, but will also be able to use their own vehicles.

Five corridors are to be set up from the Luhansk region to the city of Bakhmut, Vereshchuk wrote on a Telegram channel. On Thursday evening, Vereshchuk announced that 4,500 people had been evacuated that day. Operational safe corridors are announced daily in Ukraine, though both Russia and Ukraine have accused each other of sabotaging civilian evacuations.

The United Nations estimates the war has displaced at least 6.5 million people within the country.

The United Nations High Commissioner for Refugees (UNHCR) said that more than 4.3 million, half of them children, have left Ukraine since Russia launched its invasion on Feb. 24 and sparked Europe’s largest refugee crisis since World War II.

The International Organization for Migration (IOM) estimates more than 12 million people are stranded in areas of Ukraine under attack.

The United Nations’ humanitarian chief told The Associated Press (AP) on Thursday that he’s "not optimistic" about securing a cease-fire after meeting with officials in Kyiv and in Moscow this week, given the lack of trust between the sides. He spoke hours after Russian Foreign Minister Sergey Lavrov accused Ukraine of backtracking on proposals it had made over Crimea and Ukraine’s military status.

Two top European Union officials and the prime minister of Slovakia traveled to Kyiv on Friday, looking to shore up the EU’s support for Ukraine. Prime Minister Eduard Heger said he, European Commission President Ursula von der Leyen and EU foreign policy chief Josep Borrell have trade and humanitarian aid proposals for Zelenskyy and his government.

Part of that, Heger says is "to offer options for transporting grains, including wheat." Ukraine is a major world wheat supplier, and Russia’s war on Ukraine is creating shortages, notably in the Middle East.

Western nations have stepped up sanctions, and the Group of Seven major world powers warned that they will keep adding measures until Russian troops leave Ukraine.

The U.S. Congress voted Thursday to suspend normal trade relations with Russia and ban the importation of its oil, while the EU approved other new steps, including an embargo on coal imports. The U.N. General Assembly, meanwhile, voted to suspend Russia from the world organization’s leading human rights body.

U.S. President Joe Biden said the U.N. vote demonstrated how "Putin’s war has made Russia an international pariah." He called the images coming from Bucha "horrifying."

"The signs of people being raped, tortured, executed – in some cases having their bodies desecrated – are an outrage to our common humanity," Biden said.