Ukraine’s military says it has pulled out of areas east of rebel stronghold Luhansk under pressure from pro-Russian rebels who have, according to a military spokesman, received fresh supplies.
Ukraine’s president, Petro Poroshenko, has condemned what he alleges is Russian intervention in his country.
“We have a worsening the situation from August 27 and thousands of foreign troops and hundreds of foreign tanks are now on Ukraine’s territory,” said Poroshenko ahead of a summit meeting of EU leaders in Brussels.
“This poses a very high risk not only for the peace and stability for Ukraine but for the peace and stability in the whole of Europe,” he added.
Moscow denies direct involvement by the Russian military.
In the main rebel stronghold of Donetsk, several shells exploded near the city’s railway station on Friday damaging buildings.
One local retailer returned to her shop on Saturday.
“This morning we came here and thank God there’s something left. Other people have lost everything, everything was burned. People were left without money,” she said.
Ukraine’s interior ministry said Ukrainian fighters broke out of an encirclement of Russian-backed separatists near Donetsk on Saturday.
Other reports suggested many were still trapped.
Russian-backed forces now threaten the key port city of Mariupol.