The elimination of the last Ukrainian troops trapped in the besieged port of Mariupol would put an end to talks with Moscow, President Volodymyr Zelensky said on Saturday.

"The elimination of our troops, of our men (in Mariupol) will put an end to any negotiations" between Ukraine and Russia, Zelensky said in an interview with the Ukrainska Pravda news website. 

"That will be an impasse as we don't negotiate neither our territories nor our people."

The strategic port of Mariupol has been among the hardest hit after Russia invaded Ukraine on February 24.

Capture of the port would allow Russia to connect by land the Crimean peninsula, which it annexed in 2014, and the Moscow-backed separatist statelets in Ukraine's east.

The port was encircled by Russian troops soon after the invasion, but the outmanned and outgunned Ukrainian military have held on.

Mariupol civilians have borne the brunt of the battle, cowering in basements with no utilities for weeks.

Russian troops have gradually advanced into the city, but groups of Ukrainian forces are continuing to hold out from inside the city's giant metallurgical and heavy machinery plants, which both have a vast network of underground tunnels.