5 Ukrainian troops killed in rebel east: Military

Five Ukrainian soldiers were killed and seven wounded in the country's rebel east today in an attempt to hold back an assault by separatist forces, Ukraine's defence ministry said.

"As a result of a five-hour-long battle, four Ukrainian soldiers died, and seven more... received various injuries," spokesman for the defence ministry Dmytro Gutsulyak told a press briefing.

The battle early today took place in Lugansk region near the village of Krymske when pro-Russian separatists "attempted to overtake observation posts" on a local highway, Gutsulyak said.

Another soldier was killed in artillery fire elsewhere in the conflict zone, he added.

Ukrainian President Petro Poroshenko said Ukrainian troops were attacked with high-calibre artillery.

"The Russians... are trying to attack the positions of our troops, violating the ceasefire," he said.

Rebel officials, cited by official media in the so-called Lugansk People's Republic, the separatist enclave in Lugansk region, in turn blamed the Ukrainian army for violating the truce.

More than 10,000 people have been killed since the Moscow-backed insurgency broke out in eastern Donetsk and Lugansk regions in April 2014 following Russia's annexation of Crimea from Ukraine.

Poroshenko today apologised to the country for grossly underestimating how long the conflict would last.

"Over four years ago I declared that the anti-terrorist operation would last hours rather than months," he said.

"I am truly sorry that I gave hope which did not come true," he said.

A series of periodic truce deals, the last of which was agreed only yesterday, have helped lower violence but have not fully ended the bloodshed.

Ukraine and its Western allies accuse Russia of funnelling troops and arms across the border.

Moscow has denied the allegations despite overwhelming evidence that it has been involved in the fighting and gives open political support to the rebels.