Kiev: A "rogue" band of pro-Russian rebels was surrounding more than 100 Ukrainian troops in the eastern Lugansk region on Wednesday, the local governor said.
Several injured soldiers have been captured by the fighters, who do not answer to the main separatist leadership in Lugansk, the pro-Kiev governor Gennadiy Moskal said in a statement on his website.
"Battles are ongoing at Bakhmutka" on a road that lies west of separatist-controlled Lugansk where Ukrainian forces have several checkpoints, military spokesman Andriy Lysenko told journalists.
He denied that the Ukrainian forces were surrounded.
However, Moskal said: "We know this morning that 112 soldiers and National Guard fighters have been surrounded.
"Several injured soldiers have been captured... the situation can be characterised as critical," he added.
Moskal said attempts by representatives of the pan-European security group the OSCE to try to agree with leaders of the self-declared Lugansk People`s Republic (LNR) about ceasing fire have not brought any result.
"The attackers are fighters of the so-called Donskoy army which does not obey the LNR," he said.
The "Donskoy army" is made up of Cossacks commanded by Pavel Dremov, who told AFP late last month that he answers only to a Russian Cossack chief, not separatist leaders in eastern Ukraine.
Dremov described the September 5 truce between the separatists and Kiev as a sham and said he would not abide by the accord.
Ukrainian media accuse him of being a Russian agent.
Lysenko meanwhile also said Ukrainian forces had repelled several attacks over the past 24 hours on Donetsk airport and near the village of Debaltseve -- two constant flashpoints in the conflict in recent weeks.
Kiev and the rebels have repeatedly accused each other of violating the ceasefire agreement, with more than 300 people killed since September 5, most of them civilians.