Some women and children have been evacuated from a steel plant that is the last defensive stronghold in the bombed-out ruins of the Ukrainian city of Mariupol, while U.S. House Speaker Nancy Pelosi visited Ukraine's President Volodymyr Zelenskyy in Kyiv as a show of American support.

Russia's offensive in coastal southern Ukraine and the country’s eastern industrial heartland has Ukrainian forces fighting village by village and more civilians fleeing airstrikes and artillery shelling as the war reaches their doorsteps.

Thousands of residents were believed to remain trapped with little food, water or medicine in blockaded Mariupol. The United Nations was working to broker an evacuation of as many as 1,000 civilians who were hunkered down with an estimated 2,000 Ukrainian fighters beneath a sprawling Soviet-era steel plant that is the only part of the city not occupied by the Russians.

Footage released early Sunday by Ukrainian President Volodymyr Zelenskyy’s office showed Pelosi in Kyiv with a congressional delegation that included Reps. Jason Crow, Jim McGovern, Gregory Meeks and Adam Schiff. The visit was not previously announced.

"We believe that we are visiting you to say thank you for your fight for freedom," said Pelosi, who is second in line to the U.S. presidency after the vice president and the highest-ranking American leader to visit Ukraine since the start of the war.

"We are on a frontier of freedom and your fight is a fight for everyone. Our commitment is to be there for you until the fight is done," Pelosi added.

Pelosi’s office did not say when the meeting took place, but the light in the video and other details suggested the meeting took place Saturday. Members of Congress Barbara Lee and Bill Keating were also listed as being in the delegation, although it wasn't clear if they were in Kyiv.

The delegation was scheduled to hold a press conference in the Polish city of Rzeszow on Sunday.

Russian forces have embarked on a major military operation to seize significant parts of southern and eastern Ukraine following their failure to capture the capital. Mariupol is a major target because of its strategic location near the Crimea Peninsula, which Russia seized from Ukraine in 2014.

Russia’s RIA Novosti news agency said Saturday that 19 adults and six children were brought out from the Azovstal steelworks, but gave no further details.

A top official with the Azov Regiment, the Ukrainian unit defending the plant, said 20 civilians were evacuated during a cease-fire, though it was not clear if he was referring to the same group. There was no confirmation from the U.N.

"These are women and children," Sviatoslav Palamar said in a video posted on the regiment’s Telegram channel. He also called for the evacuation of the wounded. "We don’t know why they are not taken away and their evacuation to the territory controlled by Ukraine is not being discussed," he added.

Ukraine has blamed the failure of numerous previous evacuation attempts on continued Russian shelling.

U.N. humanitarian spokesperson Saviano Abreu said the world organization was negotiating with authorities in Moscow and Kyiv on evacuations from Mariupol, but he could not provide details of the ongoing effort "because of the complexity and fluidity of the operation."

Abreu would not confirm video posted on social media purportedly showing U.N.-marked vehicles in Mariupol.

In the town of Lyman in the Donetsk region, where at least half the population has fled Russian shelling, around 20 elderly people and children clutching bags along with their dogs and cats boarded a minivan marked with a sign reading "evacuation of children" in Ukrainian. It sped off toward the city of Dnipro as explosions were heard in the distance.

"The liberators have come and have freed us from what? Our lives?" said Nina Mihaylenko, a professor of Russian language and literature, referring to the Russian forces.

Video and images from inside the plant, shared with The Associated Press (AP) by two Ukrainian women who said their husbands are among the fighters refusing to surrender there, showed unidentified men with stained bandages; others had open wounds or amputated limbs.

A skeleton medical staff was treating at least 600 wounded people, said the women, who identified their husbands as members of the Azov Regiment of Ukraine’s National Guard. Some of the wounds were rotting with gangrene, they said.

In the video, the men said that they eat just once daily and share as little as 1.5 liters (50 ounces) of water a day among four people, and that supplies inside the besieged facility are depleted.

The AP could not independently verify the date and location of the video, which the women said was taken in the last week in the maze of corridors and bunkers beneath the plant.

The women urged that Ukrainian fighters also be evacuated alongside civilians, warning they could be tortured and executed if captured. "The lives of soldiers matter, too," Yuliia Fedusiuk told the AP in Rome.

In his nightly video address late Saturday, Ukrainian President Volodymyr Zelenskyy switched into Russian to urge Russian troops not to fight in Ukraine, saying even their generals expect that thousands more of them will die.

The president accused Moscow of recruiting new soldiers "with little motivation and little combat experience" so that units gutted early in the war can be thrown back into battle.

"Every Russian soldier can still save his own life," Zelenskyy said. "It’s better for you to survive in Russia than to perish on our land," he warned.

Meanwhile, a Russian rocket attack destroyed the airport runway in Odessa, Ukraine’s third-most populous city and a key Black Sea port, the Ukrainian army said.

Getting a full picture of the unfolding battle in eastern Ukraine has been difficult because airstrikes and artillery barrages have made it extremely dangerous for reporters to move around. Also, both Ukraine and Moscow-backed rebels have introduced tight restrictions on reporting from the combat zone.

But Western military analysts suggested that the offensive in the Donbass region, which includes Mariupol, was going much slower than planned. So far, Russian troops and the separatists appeared to have made only minor gains in the month since Moscow said it would focus its military strength in the east.

Numerically, Russia’s military manpower vastly exceeds Ukraine’s. In the days before the war began, Western intelligence estimated Russia had positioned near the border as many as 190,000 troops; Ukraine’s standing military totals about 200,000, spread throughout the country.

With plenty of firepower still in reserve, Russia’s offensive still could intensify and overrun the Ukrainians. Overall, the Russian army has an estimated 900,000 active-duty personnel. Russia also has a much larger air force and navy.

Hundreds of millions of dollars in military assistance has flowed into Ukraine since the war began, but Russia's vast armories mean Ukraine will continue to require huge amounts of support.