The Russian military has intensified its attacks on the last holdouts in the southern port city of Mariupol, hours after UN Secretary-General Antonio Guterres says he reached an agreement in principle with Russia’s leader Vladimir Putin to allow civilians in the plant to leave safely.

“To enable the safe evacuation of those civilians who want to leave, both inside the Azovstal plant and in the city, in any direction they choose and to deliver the humanitarian aid required,” Guterres said of his agreement.

Two-thousand Ukrainian soldiers and one thousand civilians are said to be hold up in bunkers underneath the sprawling structure which has been bombed repeatedly.

Meantime, Russia is suspending natural gas deliveries to certain European countries today for the first time.

Poland and Bulgaria are no longer receiving Russian fuel shipments.

Poland has played a strategic role in getting weapons and other support into Ukraine and Poland’s prime minister told the national parliament that he believes the move was revenge for new sanctions that Warsaw imposed this week against Russia.

Only Hungary has agreed to transact in rubles instead of dollars and euros.

The move by the Kremlin to up the ante comes a day after representative of the U.S., Canada and other Western allies committed to hasten the delivery of more and better military supplies to Ukraine.