Ramzan Kadyrov, the pro-Kremlin leader of Chechnya, has urged the remaining resistance fighters in the Azovstal industrial district to give up, which would all but pave the way for a Russian victory in Mariupol.

“Within Azovstal at the moment there are about 200 wounded who cannot receive any medical assistance,” he said.

“For them and all the rest it would be better to end this pointless resistance and go home to their families.”

But as Russian forces closed in on the southern port city, Ukrainian troops entered a maze-like network of underground tunnels in one final attempt to slow the invaders using guerilla tactics.

Entering the tunnels would be all but impossible and likely end in death for Russian soldiers seeking to flush out the remaining Ukrainians troops, according to military analysts.

Alexander Grinberg, an analyst at the Jerusalem Institute for Strategy and Security, told AFP: “They can try, but they’ll be slaughtered because the defenders of the tunnel will absolutely have the tactical upper hand.”

The tunnels will render Russian artillery, air strikes and snipers virtually useless, as well as surveillance efforts.

A senior US defence official said on Wednesday that Mariupol was still yet to fall, saying: “We still do not believe Russians have taken Mariupol but clearly they remain focused on that.”

Historically, outnumbered forces have been able to use networks of tunnels to outwit and outsmart their enemies.