Ukraine on Monday rejected Russian calls to surrender the port city of Mariupol, where residents are besieged with little food, water and power in a humanitarian crisis that is increasing pressure on European leaders to toughen sanctions on Moscow.

Ukraine's government defiantly rejected Russian calls for Ukrainian forces in Mariupol to lay down their arms in exchange for safe passage out of the city and humanitarian corridors to be opened from 1000 Moscow time (0700 GMT) on Monday.

"There can be no question of any surrender, laying down of arms," the Ukrainska Pravda news portal cited Ukraine's Deputy Prime Minister Iryna Vereshchuk as saying.

"We have already informed the Russian side about this...