KIEV - Ukraine has captured two Russian soldiers in its conflict with separatists in the country's east, Kiev said Sunday. Military spokesman Andriy Lysenko simply named those captured as "Russian soldiers", while giving no further details.

"Our operatives are working with them at the moment. There is no other information at the moment," Lysenko said at a press briefing.

The Ukrainian Aidar volunteer battalion has claimed it captured the two Russian troops close to the town of Shchastya, which is controlled by government forces around 15 kilometres (about nine miles) away from the rebel stronghold of Lugansk.

On its Facebook page, the battalion claimed the men captured were from Russian military intelligence, or GRU.

Three Ukrainian soldiers were killed and 17 wounded in fighting in the last 24 hours, Lysenko said Sunday. Two Ukrainian soldiers were killed in the zone close to the town of Debaltseve, a strategic railway hub that the rebels recaptured in February after a fragile ceasefire entered force.

The third soldier was killed near the town of Shchastya, Lysenko said.

"The enemy is mainly active around the town of Gorlivka," around 30 kilometres from the other separatist hub of Donetsk, Lysenko said.

"There, they have concentrated a large quantity of heavy artillery units which are bombarding our positions," he said.

The Ukrainian army has been fighting pro-Russian separatists for more than a year in a conflict that has killed more than 6,200 people.

The sides agreed a truce in February in Minsk in a deal mediated by Germany and France with Russian President Vladimir Putin present.

Kiev and the West accuse Moscow of giving support to the rebels and of having deployed its troops in eastern Ukraine.

Russia has categorically denied any arms deliveries or deployment of troops into the country.

It says that Russians fighting in the Donbass region are all volunteers, some of them troops who are on leave from their regular jobs.

Russia's opposition media has since August last year reported the apparent involvement of Russian troops in Ukraine, highlighting secret burials of Russian servicemen who apparently died in combat.

When a handful of Russian paratroopers were captured in the east in August last year, Putin said that they simply got lost while on a patrol in southern Russia.