Russian forces laid siege on two Ukrainian seaports and continued bombarding the nation’s two largest cities, Kharkiv and Kyiv, as Russia and Ukraine battle for the eighth day. 

Russia claimed control of Black Sea shipbuilding city Kherson on Wednesday and Russian troops were seen in the center of the city Thursday.

"We don’t have any Ukrainian forces in the city, only civilians and people here who want to LIVE," Kherson Mayor Igor Kolykhaev said in a statement later posted on Facebook.

TOPSHOT - Civilians walk by Ukraine residents who use an underground metro station as bomb shelter in Kyiv on March 2, 2022. - On the seventh day of fighting in Ukraine Russia claims control on March 2, 2022 of the southern port city of Kherson, street battles rage in Ukraine's second-biggest city Kharkiv, and Kyiv braces for a feared Russian assault. (Photo by Aris Messinis / STF / AFP)

TOPSHOT - Civilians walk by Ukraine residents who use an underground metro station as bomb shelter in Kyiv on March 2, 2022. - On the seventh day of fighting in Ukraine Russia claims control on March 2, 2022 of the southern port city of Kherson, street battles rage in Ukraine's second-biggest city Kharkiv, and Kyiv braces for a feared Russian assault. (Photo by Aris Messinis / STF / AFP)  ((Photo by ARIS MESSINIS/STF/AFP via Getty Images))

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As many as 300 people may have been killed as the Russians entered the city. 

Ukrainian President Volodymyr Zelenskyy, however, has said that the fighting in the city is ongoing, and a U.S. defense official also contested Russia’s claim. 

"Our view is that Kherson is very much a contested city," the official, speaking on condition of anonymity, told the Associated Press. 

Another port city, Mariupol, has come under constant attacks, according to the city’s mayor. 

Ukrainian soldiers ride in a military vehicle in Mariupol, Ukraine

Ukrainian soldiers ride in a military vehicle in Mariupol, Ukraine, Thursday, Feb. 24, 2022. Russian troops launched their anticipated attack on Ukraine on Thursday, as President Vladimir Putin cast aside international condemnation and sanctions, warning other countries that any attempt to interfere would lead to "consequences you have never seen." (AP Photo/Sergei Grits) (RuAP Photo/Sergei Grits)

"We cannot even take the wounded from the streets, from houses and apartments today, since the shelling does not stop," Mariupol Mayor Vadym Boychenko said, according to Interfax news agency.

Boychenko reported mass casualties in the city on Wednesday as it suffered intense shelling from Russian forces

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As the fighting continues, the number of people fleeing Ukraine topped 1 million Thursday, according to the United Nations’ refugee agency. The number marks the swiftest refugee exodus this century. 

In Kyiv, explosions rocked Ukraine’s capital early Thursday morning. Zelenskyy’s office attributed one explosion to a missile strike near the capital city’s southern railway station.

"Russian terrorists launched an air strike on the South Railway Station in Kyiv, where thousands of Ukrainian women and children are being evacuated," the national railway company said.

The massive Russian convoy that stalled outside of Kyiv earlier this week has meanwhile made "little discernible progress in over three days," according to Britain's defence ministry.

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In Kharkiv, Russian troops have continued battering Ukraine’s second-largest city, including with aerial attacks. Kharkiv Mayor Igor Terekhov said the city is still standing strong. 

"The city is united and we shall stand fast," Terekhov told the BBC. 

Kharkiv, Ukraine following missile attack from Russia

A view shows the area near National University after shelling in Kharkiv, Ukraine, in this handout picture released March 2, 2022. (Press service of the Ukrainian State Emergency Service/Handout )

The United Nations Human Rights Monitoring Mission in Ukraine has recorded 752 civilian casualties from the start of the invasion to midnight on March 1.

The fighting comes as a Western intelligence report on Wednesday shows that Chinese officials had at least some knowledge of Russia’s plan to invade Ukraine. The report detailed that Chinese officials called on Russia to put off the invasion of Ukraine until after the Olympics in Beijing. 

The Olympics concluded on Feb. 20 and Russian troops invaded Ukraine on Feb. 24. China has denied the report. 

Vladimir Putin and Xi Jinping

BEIJING, CHINA - FEBRUARY 4, 2022: Russia's President Vladimir Putin (L) and his Chinese counterpart Xi Jinping pose during a meeting at the Diaoyutai State Guesthouse. Alexei Druzhinin/Russian Presidential Press and Information Office/TASS (Photo by Alexei DruzhininTASS via Getty Images) (Photo by Alexei DruzhininTASS via Getty Images)

"These claims are speculation without any basis, and are intended to blame-shift and smear China," a Chinese Embassy spokesperson in Washington, D.C., told the New York Times. 

Zelenskyy struck a positive tone Thursday morning, praising Ukraine’s resistance to Russia. 

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"We are a people who in a week have destroyed the plans of the enemy," he said. "They will have no peace here. They will have no food. They will have here not one quiet moment."

"These are not warriors of a superpower," he said. "These are confused children who have been used."

The Associated Press contributed to this report.