Ukrainian President Volodymyr Zelenskyy on Thursday said thousands of people had been killed in Mariupol since Russian forces started laying siege to the strategic port city.

"Everyone knows there is a humanitarian catastrophe there," he told Belgian lawmakers in an address via video link. 

The Russian side has not yet responded to the claim.

Earlier on Thursday, Denis Pushilin, leader of the so-called Donetsk People's Republic, signed an order calling for the establishment of Donetsk's local administration in the city, days after he claimed his forces have controlled the central region in Mariupol.

(With input from Reuters)