Poroshenko's video statement.
More than the 4,000 estimated by Aleksander Zakharchenko, the pro-Russian rebel leader in eastern Ukraine.
Daniel Baer is the U.S. ambassador to the OSCE.
More from our news desk on Poroshenko's statement:
Ukrainian President Petro Poroshenko says a Russian military invasion of his country has occurred following reports that the southeastern border town of Novoazovsk has fallen to Russian troops.
Poroshenko canceled a planned trip to Turkey on August 28 and said he is convening an emergency meeting of the National Security and Defense Council to discuss the "sharp deterioration" of the situation in the Donetsk region.
The council said on Twitter on August 28 that Russian troops had seized control of Novoazovsk and several settlements in the Novoazovsk, Starobeshevskiy, and Amvrosiyivskiy districts.
The council said Ukrainian troops near Novoazovsk came under attack by Grad missile systems fired from Russian territory before being attacked by two convoys of Russian armor in Ukraine.
Western officials have accused the Russian military of directly intervening in eastern Ukraine.
Moscow has long denied arming the rebels or sending troops into Ukraine.
BREAKING: Ukrainian President Petro Poroshenko says a Russian military invasion has occurred and that he is convening an emergency meeting of the National Security and Defense Council to discuss the crisis. He has canceled a trip to Turkey.
BREAKING: Ukraine's Security and Defense Council says on Twitter that Russian troops have seized control of the border town of Novoazovsk. The town's mayor earlier said that pro-Russian fighters had entered the town with support from dozens of armored vehicles.