UNITED NATIONS, April 13 -- UN Security Council opened an emergency meeting Sunday night in response to rising tensions in eastern Ukraine after pro-Russian militia seized government buildings there.

Joy Ogwu, the Nigerian permanent representative to the United Nations who holds the council's rotating chair for April, opened meeting here at around 8:05 p.m. EDT (0005 GMT Monday).

The meeting is open to press although Ogwu had said previously that the meeting would be held behind closed doors.

It is the 10th time that the 15-nation UN body met in a bid to address the Ukraine crisis since February. The UN General Assembly took up the issue on March 27.

"Following close to two weeks of relative calm, starting on 6 April, armed individuals and separatist groups began to seize government buildings and confiscate lethal weapons in the Donetsk Oblast of Ukraine, including in the cities of Donetsk, Lugansk and Kharkiv," Oscar Fernandez Taranco, the UN assistant secretary-general for political affairs, said in opening remarks at the meeting.

"It has now been reported that there have been at least five new cities in eastern Ukraine targeted by uprisings and seizures of government buildings in the last twenty-four hours, including the towns of Sloviansk, Kramatorsk and Druzhkivka," he said.

"The situation is therefore now more combustible than ever," he said.

"The secretary-general and the United Nations remain committed to the pursuit of a peaceful solution to this ever deepening crisis."

As the meeting was underway, Kiev declared the launch of a "full-scale anti-terrorist operation" in the eastern part of the country.

UN Secretary-General Ban Ki-moon, in a statement issued here late Saturday, voiced his deep concerns at the seriously deteriorating situation in eastern Ukraine and appealed to all sides to work toward calming the situation there, which has the "growing potential" to spark violent clashes.