The EU President Donald Tusk has condemned “Russian aggression” for the deaths of five Ukrainian servicemen who were killed when pro-Russian rebels attack government positions in the Luhansk region on Thursday.
Four of the men died during an eight-hour clash near Krymsky, a village around 30 miles west of Luhansk.
Ukrainian forces said they killed eight rebels.
“Five of our soldiers have died over the past 24 hours,” said Oleksandr Turchynov, chief of Ukraine's National Security and Defence Council, said in televised remarks.
He added “a conflict situation is under way between various criminal groups that make up the occupational administration on the occupied territories.”
The situation in Luhansk escalated after a power-struggle between separatist factions controlling the city.
Men carrying rifles blocked access to administrative buildings in the city just hours after rebel leader, Igor Plotnisky, fired interior minister, Igor Kornet.
The men blocked access to some buildings under orders from the interior ministry, according to AFP.
A peace agreement put in place almost three years ago has failed to cease fighting in eastern Ukraine, with each side accusing the other of violating the terms of a ceasefire.
According to UN figures, more than 10,000 people have died in the conflict in eastern Ukraine since it erupted in April 2014, shortly after Russia annexed the Crimea Peninsula.
More than 1.6 million people have been displaced.
