Russian President Vladimir Putin said on Tuesday that Moscow's military operation in Ukraine would undoubtedly achieve what he said were its "noble" objectives. Putin's remarks were made as Russian troops were aiming to take control of the city of Mariupol, part of an anticipated massive onslaught across eastern Ukraine, as defending forces tried desperately to hold them back.

Speaking at an awards ceremony at the Vostochny Cosmodrome in the Russian Far East, Putin was quoted as saying by Russian news agencies that said Moscow had no other choice but to launch a military operation to protect Russia and that a clash with Ukraine's anti-Russian forces had been inevitable.

"Its goals are absolutely clear and noble," Putin said of Russia's military campaign.

Putin said the main objective of Moscow's military intervention in Ukraine was to save people in the Donbass region of eastern Ukraine, where Russian-backed separatists have been fighting Ukrainian forces since 2014.

"On the one hand, we are helping and saving people, and on the other, we are simply taking measures to ensure the security of Russia itself," Putin said. "It's clear that we didn't have a choice. It was the right decision."

With the offensive of Mariupol, Russia is believed to be trying to connect occupied Crimea with Moscow-backed separatist territories Donetsk and Lugansk in Donbass, and has laid siege to the strategically located city, once home to more than 400,000 people.

Ukrainian forces were "surrounded and blocked," tweeted Myhaylo Podolyak, an official from Ukrainian President Volodymyr Zelenskyy's office.

But on Monday the Ukrainian army insisted that "the defense of Mariupol continues."

"The connection with the units of the defence forces that heroically hold the city is stable and maintained," the Land Forces of Ukraine wrote on Telegram.

In his nightly address, Zelenskyy made another plea to his allies for more weapons to boost the defense of the city.

"We are not getting as much as we need to end this war sooner. To completely destroy the enemy on our land ... in particular, to unblock Mariupol," he said.

He made a similar appeal for military assistance to South Korea's National Assembly earlier in the day, telling lawmakers Russia had "completely destroyed Mariupol and burned it to ashes."

"At least tens of thousands of Mariupol citizens must have been killed," he added.

Chemical weapon allegations

Late Monday, Britain said it was trying to verify reports that Russia had also used chemical weapons in the city.

Western officials have previously expressed concerns that as the conflict drags into its seventh week, Russia could resort to such extreme measures.

Ukrainian lawmaker Ivanna Klympush said Russia had used an "unknown substance" and that people were suffering from respiratory failure.

But on messaging app Telegram, Petro Andryushchenko, an aide to the city's mayor, wrote that a chemical attack was not confirmed and that they were "waiting for official information from the military."

Elsewhere in the east, the heavy bombardment continued as civilians were urged to flee ahead of an expected Russian troop surge in the region.

Eight people were killed by shelling in the northeastern city of Kharkiv, Oleg Synegubov, the head of the regional state administration, said.

"Our Armed Forces firmly hold the defensive positions of Kharkiv and the region," he wrote on his Telegram channel.

"That is why the Russian enemy continues to 'fight' with the civilian population due to its powerlessness."

Russian forces are reinforcing around the Donbass region, notably near the town of Izyum but have not yet launched a full offensive, Pentagon officials said Monday.

They reported a Russian convoy had been observed heading for Izyum, an hour's drive north of Kramatorsk, saying it appeared to be a mix of personnel carriers, armored vehicles and possible artillery.

Ukraine's Defense Ministry said it believed a major assault would happen soon.

"We don't know precisely when, but the preparation is almost over," spokesperson Oleksandr Motuzyanyk told a briefing on Monday.

'Logic of war'

Such signs of a buildup in Donbass suggest hopes of an imminent diplomatic solution remain slim.

After a meeting with Putin on Monday, Austrian Chancellor Karl Nehammer said he was "rather pessimistic" of such efforts succeeding as Putin had "massively entered into a logic of war."

Ukraine's allies are trying instead to increase economic and diplomatic pressure on Moscow – but EU foreign ministers' discussions on a sixth round of sanctions on Monday ended without a consensus.

"Nothing is off the table, including sanctions on oil and gas," Josep Borrell, the European Union's top diplomat, told reporters after the meeting. "But today, no decision was taken."

The European police agency Europol, meanwhile, said Monday it had launched an operation targeting the assets of Russian individuals and companies sanctioned over the war.

In an effort to shore up wider international support for Kyiv, U.S. President Joe Biden held virtual talks with Indian Prime Minister Narendra Modi just weeks after saying New Delhi had been "shaky" in its response to the invasion.

"There were conversations about how to mitigate the destabilizing impacts of Putin's war, including on food supply, where India is in a position to assist," a U.S. official said.

And the U.N. Security Council – which on Monday held a session on the plight of women and children in Ukraine – will hold another meeting next week on the humanitarian situation there, in a bid to keep pressure on Russia despite its veto power over the body, diplomats said.

'Rape and sexual violence'

At Monday's Security Council meeting, officials called for an investigation into violence against women during the conflict.

"This war must stop. Now," Sima Bahous, director of the U.N. women's agency, told the meeting.

"We are increasingly hearing of rape and sexual violence. These allegations must be independently investigated to ensure justice and accountability."

More than 4.5 million Ukrainian refugees have now fled their country, the United Nations refugee agency said – 90% of them women and children.

Russian troops have been accused of widespread atrocities across the country, particularly in areas around Kyiv from which they have now withdrawn, allegations Moscow categorically denies.

Ukraine says more than 1,200 bodies have been found around the capital, with authorities pursuing "500 suspects," including Putin and other top Russian officials.

Seven bodies were found Monday under the rubble of two multistory buildings in the town of Borodianka, the state emergency service said, bringing the total to 19.

Lithuania's prime minister, who was touring the town, said she had "no words" to describe the devastation and accused Russia of war crimes.

"The images of the ruined Ukrainian towns and cities, and the testimonies of the survivors, reveal the real face of Russia," Ingrida Simonyte said.

French investigators have arrived in Ukraine to help probe suspected war crimes, and the European Union has earmarked 2.5 million euros ($2.7 million) to the International Criminal Court (ICC) for future Ukraine cases.

The global consequences of the war were evident Monday as the World Trade Organization (WTO) projected world trade growth could almost halve this year.

The WTO said the conflict was a "severe blow" to the world's economy which in the longer term could even spark a disintegration of the global economy into separate blocs.

Russia was also blamed for an escalating global food crisis by the EU's Borrell because of its bombing of wheat stocks and preventing ships from carrying grain abroad.