Conflict raged near Kyiv on Saturday and Ukrainian officials said heavy shelling and threats of Russian air attacks were endangering attempted evacuations of desperate civilians from encircled towns and cities elsewhere.

Ukrainian President Volodymyr Zelensky said Russia was sending in new troops after Ukrainian forces had put 31 of its battalion tactical groups out of action in what he called Russia’s largest army losses in decades. He gave no details and it was not possible to verify either statement.

Zelensky also said he had spoken to German Chancellor Olaf Scholz and French President Emmanuel Macron about pressuring Russia to release the mayor of the city of Melitopol, who Ukraine says was kidnapped on Friday by Russian forces.

More than 2,000 residents of the southern city, which is now under Russian control, protested outside the city administration building to demand the release of the mayor, Ivan Fedorov, Kyrylo Tymoshenko, deputy head of the President’s office, said.

A call between Scholz, Macron and Russian President Vladimir Putin was underway, the French presidency said. Russia has not commented on the fate of Fedorov, who Ukrainian officials said was kidnapped by Russian forces on false accusations of terrorism.

Zelensky said his country could not stop fighting but was upholding a ceasefire around an agreed humanitarian corridor out of the southern port of Mariupol, which has been under an almost two-week siege, and called on Russia to do the same.

Putin launched the invasion on February 24 in an operation that has been near universally condemned around the world and that has drawn tough Western sanctions on Russia.

The bombardment has trapped thousands of people in besieged cities and sent 2.5 million Ukrainians fleeing to neighbouring countries.

Air raid sirens blared across most Ukrainian cities on Saturday morning urging people to seek shelters, local media reported.

The exhausted-looking governor of Chernihiv, around 150km northeast of Kyiv, gave a video update in front of the ruins of its Ukraine Hotel, which he said had been hit on Saturday.

“There is no such hotel any more,” Viacheslav Chaus said, wiping tears from his eyes. “But Ukraine itself still exists, and it will prevail.”

Russian rocket attacks destroyed a Ukrainian airbase and hit an ammunition depot near the town of Vasylkiv in the Kyiv region on Saturday morning, Interfax Ukraine quoted Vasylkiv mayor

Natalia Balasynovych as saying.

Moscow has denied targeting civilians what it calls a special operation to demilitarise Ukraine and unseat leaders it refers to as neo-Nazis. It has not responded to Ukrainian challenges to provide evidence.

Ukraine said it expected a new wave of attacks on the regions around the capital Kyiv, the country’s second city Kharkiv and Donbass in the east, where Russian-backed separatists have expanded their control.

Britain’s defence ministry said on Friday that Russian forces could launch an offensive on Kyiv in a few days. In an update on Saturday, it said fighting northwest of the capital continued, with the bulk of Russian ground forces 25km from the centre.