Russia has lost up to 40 per cent of the units it sent into Ukraine when it invaded its neighbour in February, says the Ukrainian military’s general staff.

The troops were either completely destroyed or have lost their combat capabilities, he said at the daily bulletin, but did not give concrete numbers.

The information could not be verified independently.

The area surrounding embattled Mariupol continued to face the most serious situation. The Russian army was attempting a blockade of the city from the western and eastern fringes of the port city, but was suffering “significant losses,” according to the bulletin.

Ukrainian authorities said some 20,000 people from Mariupol, on the Sea of Azov, managed to get to safety on Tuesday.

About 30,000 civilians nationwide were able to leave threatened areas on Tuesday, but a column with relief supplies for Mariupol was still blocked by Russian soldiers, Ukrainian President Volodymyr Zelensky said.

In the Odessa region, Russian ships were shelling the Ukrainian coast but there was no attempt to land, Interior Ministry adviser Anton Herashchenko said.

Ukrainian and Russian representatives are set to resume their negotiations on Wednesday.

Mr Zelensky said demands were starting to get more realistic, while warning it would still take a while before Ukraine can be satisfied with talks.

Meanwhile the prime ministers of Poland, the Czech Republic and Slovenia assured Mr Zelensky of their solidarity and support during a visit to Kiev. They travelled to Kyiv by train in a gesture of support for Ukraine.