|Ukraine says rebel forces (pictured) are being helped by regular Russian troops|
Ukraine's military says its forces have captured two Russian soldiers fighting with rebels in eastern Ukraine.
The troops were seized in the town of Shchastya, near the line of separation.
A video emerged apparently showing one of the soldiers - which it said were members of Russia's elite special forces - saying during questioning that he was a sergeant from the central Russian city of Togliatti.
Russia denies claims that it is sending its forces to help the rebels.
However, it admits that a number of Russian nationals are fighting with the separatists in Ukraine's eastern Luhansk and Donetsk regions.
More than 6,000 people have been killed in fighting which began in April 2014 when the rebels seized large parts of the two regions.
This happened a month after Russia annexed Ukraine's southern Crimea peninsula.
'Special forces brigade'
On Sunday, Ukrainian military spokesman Andriy Lysenko said that the two Russian soldiers were captured by the volunteer Aydar battalion in Shchastya, Luhansk region.
He said this happened close to the front line, without giving further details.
Meanwhile, Ukrainian MP Anton Gerashchenko posted a video purportedly showing the questioning of one of the seized soldiers, who was injured during the fighting.
The soldier identifies himself as Aleksandr Aleksandrov - a sergeant in the third special forces brigade.
He says he was part of a 14-member group, naming the commander and his deputies.
The video has not been independently verified. Russia has not publicly commented on the latest developments.
Ukraine and the West have repeatedly stated than thousands of Russia's regular troops are deployed in the Donetsk and Luhansk regions. Last year, the Kiev authorities posted a video apparently showing Russian paratroopers seized in the region.
Earlier this week, Russian opposition activists published a report, originally compiled by murdered Kremlin critic Boris Nemtsov, alleging that 220 Russian soldiers had died in two key battles in eastern Ukraine.
The lull in the conflict in eastern Ukraine since February's ceasefire has been punctuated by frequent violations.
Truth has been the first casualty in this war, without question. Perhaps the most remarkable characteristic of this war has been President Putin's extraordinary ability to look the world in the eye and lie blatantly, knowing all the while that no-one in the world believes a word he says.
This is classic bullying. Incredibly immature, but it works in the short term. The schoolyard bully claims the little guy's lunch is his and just takes it daring the little guy to do something about it. Most often, the little guy does nothing because there is nothing he can do by himself. His friends and classmates watching, choose not to get involved and turn away.
It's a pity that none of Ukraine's friends, if it has any real friends, were willing to send 'little brown men' in to the Crimea last year to counter the 'little green men', known to be Russian soldiers. You don't appease a bully and expect him to stop. He will only stop when he is confronted by someone(s) willing to stand up to him.
The west hasn't completely failed Ukraine, but it's close. The sanctions applied to Russia are affecting its economy, but the drop in oil prices are doing as much, if not more, than the sanctions.
Yet, Putin's genius for knowing his people has kept him as popular as ever. Sanctions won't work until there is pressure on Putin by his own people. The bully's own friends have to turn on him. Fear of an uprising is the only thing that will affect him. It doesn't look like that will occur any time soon.
The situation in eastern Ukraine
Fewer clashes but still occurring daily, with intense fighting around port city of Mariupol
Ukrainian government says it has lost full or partial control of 28 towns and villages since February
Both sides accuse each other of building up weaponry for a new offensive