Ukraine's president has accused Russian forces of sending troops into Ukraine. The country's security and defense council said Russian troops have seized control of a key southeastern border town.
President Petro Poroshenko said on Thursday that Russian troops had been sent Ukraine, prompting him to cancel a trip to Turkey.
"I made the decision to cancel a working visit to the Republic of Turkey in connection with the rapidly deteriorating situation in the Donetsk region…as an incursion of Russian forces has taken place," he said in a statement on the presidential website.
Ukraine's National Security and Defense Council said earlier on Twitter that Russian troops had taken control of Novoazovsk, a town that lies along the road connecting Russia to the Russia-annexed Crimean peninsula. A number of surrounding villages had also been seized, they said.
There has been increasing concern in Kyiv and the West about Russia's possible direct participation in the conflict, despite Moscow's repeated denials of allegations that its troops are on the ground.
The US ambassador in Kyiv earlier accused Russia of being "directly involved" in fighting.
"An increasing number of Russian troops are intervening directly in fighting in Ukrainian territory," Geoffrey Pyatt wrote on Twitter. He said Moscow was "directly involved in the fighting" and had sent in its "newest air defense systems including the SA-22."
The US mission to the Organization for Security and Cooperation in Europe said it would hold an extraordinary meeting Thursday following reports that Russian troops were on the ground backing the rebels. The news was confirmed on Twitter.
hc/tj (Reuters, AFP, AP)