The situation in Ukraine is worsening in the eastern city of Mariupol, the site of heavy shelling. The country has turned down a Russian call to surrender the city.

Russia's Defense Ministry has issued a statement saying Ukrainian forces who lay down their arms will be guaranteed safe passage out of Mariupol and that humanitarian corridors will open.

Ukraine refused the offer. The media cited the deputy prime minister as saying, "There can be no question of any surrender."

Heavy fighting continues in Mariupol.

The city council says Russian forces have bombed an art school where about 400 residents were taking shelter. Women, children and elderly people remain trapped under the rubble.

A theater where many residents took refuge was also destroyed last week. Hundreds are reportedly still under the rubble.

On Saturday, the city council accused Russian forces of transporting more than 1,000 civilians across the border against their will.

Ukrainian President Volodymr Zelenskyy spoke with CNN on Sunday. He reiterated his willingness to negotiate with Russian President Vladimir Putin.

He added he would be willing to take a chance "if there is just a one percent chance to stop this war."

But he warned the conflict would develop into to ''a third World War" if negotiations were to fail.

But Russia is showing no signs of easing back on its offensive. The military has used its Kinzhal hypersonic missile for two consecutive days.

There is growing concern among the US and other Western countries that Russia may resort to the use of biological and chemical weapons.

In other developments, the mayor of Enerhodar in southeastern Ukraine says the city's deputy mayor Ivan Samoidiuk has been abducted by Russian forces.

Enerhodar is the site of the Zaporizhzhia nuclear power plant which has been seized by Russia's military. It's one of the largest facilities of its kind in Europe.

Two mayors were kidnapped by Russian forces this month in the same region.