By Max Hunder KYIV (Reuters) -Ukraine said on Saturday it had recaptured a swathe of the battlefield city of Sievierodonetsk, in a rare counter-offensive against Russia’s main assault force that had been steadily advancing in the east. The Ukrainian claim could not be independently verified, and Moscow said its own forces were making gains there. But it was the first time Kyiv has claimed to have launched a big counter-attack in Sievierodonetsk after days of yielding ground there. Russia has concentrated its forces on Sievierodonetsk in recent weeks for one of the biggest ground battles of the…