Russian troops were in the centre of the Ukrainian port of Kherson on Thursday after a day of conflicting claims over whether Moscow had captured a major urban centre for the first time in its eight-day invasion.
Russia's defence ministry said it had captured Kherson on Wednesday but an adviser to Ukrainian President Volodymyr Zelenskiy responded that Ukrainian forces continued to defend the Black Sea port of about 250,000 people.
"We are a people who broke the enemy's plans in a week," Zelenskiy said in a video address. "These plans had taken years to write - they are mean, with hatred for our country, for our people."
The capture of the strategic southern provincial capital, where the Dnipro River flows into the Black Sea, would be the first significant urban centre to fall since Moscow launched its invasion on February 24.
Russian forces have yet to overthrow the government in Kyiv but thousands are reported to have died or been injured and more than a million people have fled Ukraine amid the biggest attack on a European state since 1945.
"For many millions more, inside Ukraine, it’s time for guns to fall silent, so that life-saving humanitarian assistance can be provided," UN High Commissioner for Refugees, Filippo Grandi said in a tweet.
Russia's attack has led to a barrage of international sanctions that threaten the global economic recovery from the COVID pandemic, and stoked fears of wider conflict as Western countries send arms to help the Ukrainian military.
Kherson Mayor Igor Kolykhayev said late on Wednesday that Russian troops were in the streets and had entered the council building. He called on civilians to walk through the streets only in daylight and in ones and twos.
"There were armed visitors in the city executive committee today," he said in a statement. "I didn't make any promises to them ... I just asked them not to shoot people."
The US State Department called on Putin and the Russian government to "immediately cease this bloodshed" and withdraw forces from Ukraine. It also accused Moscow of launching a "full war on media freedom and the truth" by blocking independent news outlets and social media to prevent Russians from hearing news of the invasion of Ukraine.
Russia calls its actions in Ukraine a "special operation" that is not designed to occupy territory but to destroy its neighbour's military capabilities and capture what it regards as dangerous nationalists.
It denies targetting civilians although there have been widespread reports of civilian casualties and the shelling of residential areas.
Bombing in Kharkiv, a city of 1.5 million people, has left its centre a wasteland of ruined buildings and debris.
Russians have shelled the city of Izyum, about 120 km southeast of Kharkiv, killing six adults and two children, Ukraine's parliament said. Reuters was unable to verify the casualties.
The UN Human Rights Office has confirmed the deaths of 227 civilians and 525 injuries during the conflict as of midnight on March 1, cautioning that the real toll would be much higher due to reporting delays.
An explosion also rocked the Kyiv railway station where thousands of women and children were being evacuated. The blast was caused by wreckage from a downed Russian cruise missile, a Ukrainian interior ministry adviser said, and there were no immediate reports of casualties.
An investigation into possible war crimes will immediately be opened by the International Criminal Court, following requests by 39 of the court's member states, an unprecedented number.