The International Committee of the Red Cross, which for days has been trying to get a team to Mariupol to help provide safe passage for thousands of civilians seeking to leave, said on Monday its staff had been stopped in the nearby town of Mangush, currently under Russian control.

The team "that was held by police in Mangush on Monday was released last night", the Geneva-based organisation said in a statement, adding, "This is of great relief to us and to their families."

"The team is focused now on continuing the humanitarian evacuation operation," it said.

"This incident yesterday shows how volatile and complex the operation to facilitate safe passage around Mariupol has been for our team, who have been trying to reach the city since Friday."

Mariupol has been under siege from Russian forces for over a month, leaving the population to fend for themselves in conditions which have been denounced by the international community.

Previous attempts to evacuate residents have collapsed, although some have made the dangerous dash to freedom alone from the city, which housed approximately half a million people before the war began.

Mariupol's mayor said on Monday a full 90 percent of the city had been destroyed. He said around 130,000 people remained trapped there, as it continued to be pounded by Russian bombardments.