UNITED NATIONS, United States - The UN Security Council is to hold an emergency meeting on Thursday on the Ukraine crisis following reports that Russia had sent hundreds of troops to shore up separatists in east Ukraine.
The session requested by Lithuania will be held at 1600 GMT at UN headquarters in New York.
"Russia will be asked to explain why it has its troops inside Ukraine," British Ambassador Mark Lyall Grant, whose country holds the presidency of the Security Council, told journalists.
"It's very clear that Russian regular troops are now in Ukraine."
NATO said at least 1,000 Russian troops were on the ground supporting pro-Kremlin separatists who have been fighting Kiev's rule since April, but Russia insisted none of its soldiers were on Ukrainian soil.
Kiev said Russian troops on Wednesday seized control of the key border town of Novoazovsk and a string of surrounding villages along the southeastern strip of the frontier.
Ukraine's military also claimed a Russian battalion had set up its headquarters near a village in the same area.