Hundreds of protesters have descended on the centre of Kherson on Saturday days after the city was captured by the Russian military.

       Footage posted on social media showed hundreds of Ukrainians waving flags, singing and chanting in the southern port city as the war continued.

       In one video, a small number of troops can be seen facing the peaceful protest and firing shots into the air, but it does little to disperse the crowd.

       Another video appears to show a protester who had climbed on top of a moving Russian armoured vehicle while waving the Ukrainian flag.

       The show of defiance came as Russia claimed its forces had stopped firing near two Ukrainian cities, Mariupol and Volnovakha, to allow safe passage to civilians fleeing the fighting.

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       However, Ukraine has now said the evacuation of Mariupol has been postponed, accusing Russian troops of breaching the ceasefire by shelling along the evacuation route.

       The government had earlier said the plan was to evacuate around 200,000 people from Mariupol and 15,000 from Volnovakha.

       Russian forces have continued to surge ahead in other parts of Ukraine and are focusing on Kyiv, the capital city, and Kharkiv, the country’s second-largest city.

       A 40-mile Russian military convoy that has now stalled outside Kyiv was again under attack, with explosions audible from the city centre.

       At the southeastern port city of Mariupol, mayor Vadym Boychenk has warned there is no water, heat or electricity and food is running out.

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       Video appears to show Ukrainian protester on top of moving Russian vehicle

       This map shows the extent of Russia’s invasion of Ukraine

       (Press Association Images)

       Ukrainian artillerymen keep position in the Luhansk region

       (AFP via Getty Images)

       In a statement on Saturday, Ukraine’s military said that armed forces “are fighting fiercely to liberate Ukrainian cities from Russian occupiers,” counterattacking in some areas and disrupting communications.

       Ukrainian president Volodymyr Zelensky was expected to press Washington for more help in a video call with the US Senate later on Saturday.

       Meanwhile, on Friday Russia escalated its crackdown on dissent in its own country after its parliament passed a law imposing a prison term of up to 15 years for spreading intentionally “fake” news about the military.

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       “This law will force punishment - and very tough punishment - on those who lied and made statements which discredited our armed forces,” said Vyacheslav Volodin, the chairman of the Duma, Russia’s lower house of parliament.

       Russia has also blocked Facebook for restricting state-backed channels and the websites of the BBC, Deutsche Welle and Voice of America.

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       Additional reporting by Reuters