Ukrainian government sources have told the BBC that they believe that Russian troops are continually entering and leaving eastern Ukraine.

According to some claims there could be at least 18,000 involved, despite last month's ceasefire agreement which requiring all foreign troops to leave the region.

At least 6,000 people are believed to have been killed since the conflict in the eastern Donetsk and Luhansk regions erupted last April.

Russia denies accusations that it is helping the rebels.

Richard Galpin reports.