A theatre in the Ukrainian city of Mariupol where hundreds of people were sheltering has been destroyed by Russian forces, local officials have said.

People are feared to have been hiding inside when the building was attacked today and the number of casualties is not yet known. 

Inna Sovsun, a Ukrainian MP, told CNN that thousands of people had been sheltering there in the past two weeks.

Mariupol, a port city of 420,000 people near the Russian border, has been under almost constant bombardment for two weeks. It has become a symbol of resistance and the human cost of President Putin’s war on Ukraine.

According to the RIA news agency, Russia's Defence Ministry has denied it carried out the attack, instead a far-right Ukrainian militia, of blowing it up, but gave no evidence to back up the claims.

Earlier, Ukrainian presidential adviser Mykhailo Podolyak said that a "radical change" had occurred between Ukrainian and Russian forces after Kyiv launched counter offensives in "several operational areas".

He added that it has substantially altered the "parties' dispositions", without elaborating further.