Ukraine's Petro Poroshenko said a strong EU response is needed because his country is subject to "military aggression and terror."
"Thousand(s) of the foreign troops and hundreds of the foreign tanks are now on the territory of Ukraine," Poroshenko told reporters, speaking in English. "There is a very high risk not only for peace and stability for Ukraine but for the whole peace and stability of Europe."
EU Commission President Jose Manuel Barroso said before a summit of the 28-nation EU's leaders in Brussels that "sanctions are not and end in themselves" but a means to dissuade Russia from further destabilizing Ukraine.
"The opening of new fronts and the use of Russian regular forces (on Ukrainian soil) is not acceptable and represents a grave transgression," Barroso added.
NATO estimates that at least 1,000 Russian soldiers are in Ukraine even though Russia denies any military involvement in the fighting that has so far claimed 2,600 lives, according to UN figures.
Conceding ground in the face of a reinvigorated rebel offensive, Ukraine said today that it was abandoning a city where its forces have been surrounded by rebels for days. It was also pulling back from another it had claimed to have taken control of two weeks earlier.
