Russia and Ukraine both confirm that fighting is taking place inside the city center of the heavily occupied port city of Mariupol in southeastern Ukraine.

- There are street fights in the city center, says Mayor Vadim Bojtjenko to the BBC.

He testified about shelling from tanks, artillery and all kinds of weapons.

The city is surrounded by Russian forces, and the residents have no access to electricity, gas or water, he says.

- Our forces do everything they can to keep the positions in the city, but the enemy's forces are unfortunately much greater.

Police appeal to Macron and Biden

If one takes Mariupol, where some of the worst suffering during the war took place, it would be a great success on the battlefield for the Russians.

They have largely got stuck outside major cities, over three weeks after the largest land invasion in Europe since World War II began, writes AP.

- Children and the elderly die.

The city is destroyed and obliterated from the face of the earth, says police Michail Vershnin in a video on Twitter.

In the clip, he stands in front of the damaged port city and appeals to US President Joe Biden and Frenchman Emmanuel Macron.

- You have promised us help.

Give it to us now.

You are great leaders, Macron and Biden.

It was until the end, says Vershnin.

Tens of thousands are waiting

Around 40,000 have managed to leave Mariupol in the past five days, according to Mayor Vadim Boychenko.

About 20,000 are waiting to be evacuated.

Ukraine announced on Saturday that it has an agreement with Russia on ten humanitarian corridors, including one from Mariupol.

But several such agreements have previously proved to be meaningless.

On Saturday, fierce fighting broke out in the city at the giant Azovstal steelworks, according to a spokesman for the Ukrainian Interior Ministry:

- I can say that we have lost this economic giant.

One of Europe's largest metallurgical plants is being destroyed.

Four hotbeds of unrest

The Ukrainian authorities have not noticed any decisive movements of the front line in the last 24 hours, according to Presidential adviser Oleksiy Arestovych.

He says fighting is underway, pointing to the southeastern city of Mariupol, the southern cities of Mykolaiv and Kherson, and the eastern city of Izium as special hotspots, according to Reuters.

Hard to reach

Constant shelling hinders the work of the rescue service and makes it difficult for aid organizations to reach.

- The challenge is to enter cities that are surrounded or about to be surrounded, says Jakob Kern, emergency coordinator at the UN Food Program (WFP), to AFP and describes the situation as "terrible".

According to him, it is practically impossible now to arrange food supplies to Mariupol and the cities of Kharkiv and Sumy in the northeast.