As Russian forces pummel Ukrainian cities and towns into rubble, setting off a mass exodus of panicked people and creating increasingly dire conditions for those who remain, the prospect of a limited ceasefire in one besieged coastal city collapsed under the hail of reported Russian shelling on Saturday.

President Vladimir Putin also threatened that Ukraine might lose its statehood. “The current leadership needs to understand that if they continue doing what they are doing, they risk the future of Ukrainian statehood,” he said at a meeting in Moscow on Saturday. “If that happens, they will have to be blamed for that.”

Putin said the western sanctions were akin to war. “These sanctions that are being imposed are akin to a declaration of war but thank God it has not come to that,” he said.

About half a million people in the Ukrainian city of Mariupol were entering their third day without heat, electricity or water when the ceasefire was announced, but a partial evacuation was quickly halted amid what Ukrainian officials said was renewed shelling.

As Russia tightened its hold on some major cities, fearful residents are fleeing west, adding to the fastest-moving flow of refugees in Europe since the end of World War II, the head of the United Nations refugee agency said on Saturday.

Putin is further tightening state control over information about the war, and it remains unclear how much information people in Russia are seeing at a time the country’s isolation is intensifying. On Saturday, Russia’s state airline Aeroflot said it would suspend all international flights from March 8 “due to additional circumstances that prevent the performance of flights”.

Russia’s military is trying to add to its gains in the south, moving closer to the vital port city of Odessa, as it tries to cut off the Ukrainian government from the sea.

Outside Kyiv, there have been fierce attacks and counterattacks as Ukrainian forces battle to keep the Russians from encircling it. The vast armed convoy approaching Kyiv from the north still seems to be largely stalled, according to western analysts.

Since Russian forces surrounded Mariupol this week, the city has been facing a growing humanitarian crisis. It is largely impossible to bring in medical supplies and other relief. Despite daily bombardments, the local government has refused to surrender.

Popular street protests are presenting a challenge to the new authority in the southern Ukraine city of Kherson, the first major city to fall to Russian forces.

Around 10am on Saturday, people started gathering in Liberty Square, the central square in the city centre, according to video streamed live by protesters at the scene. There appeared to be hundreds of people, chanting and holding Ukrainian flags.

One video verified by The New York Times showed a man on top of a Russian armoured personnel carrier, waving a Ukrainian flag as it drove down the street, prompting cheers from onlookers.