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WRAPUP 11-Ukraine reports battlefield gains as Europe's energy worries grow

(Adds Ukrainian general staff quote, German reaction to Gazprom Germania sanctions)

* Russia imposes sanctions on Gazprom units in Europe, U.S.

* Ukraine halts major route for Russian gas to Europe

* Ukrainian forces seek to cut Russian battlefield supply lines

* Kremlin: Kherson residents can decide whether to join Russia

* Mariupol steelworks under bombardment again

By Pavel Polityuk and Jonathan Landay

KYIV/VILKHIVKA, Ukraine, May 11 (Reuters) - Ukraine on Wednesday reported pushing back Moscow's forces in a counterattack that could signal a shift in the momentum of the war and shut gas flows on a route through Russian-held territory, raising the spectre of an energy crisis in Europe.

Ukraine's armed forces' general staff said it had recaptured Pytomnyk, a village on the main highway north of the second largest city of Kharkiv, about halfway to the Russian border.

"The occupying forces moved to the defence in order to slow down the pace of the offensive of our troops," it said. "The settlement of Pytomnyk ... was liberated."

Following days of advances north and east of Kharkiv, one Ukrainian military source said on condition of anonymity that Ukraine's forces were within just several kilometres of the Russian frontier by Wednesday morning.

Beforehand, Russian forces had been on the outskirts of Kharkiv, a city 40 km (25 miles) from the frontier.

The advance appears to be the fastest that Ukraine has mounted since it drove Russian troops away from the capital Kyiv and out of northern Ukraine at the beginning of April.

If sustained, it could let Ukrainian forces threaten supply lines for Russia's main attack force, and even put rear logistics targets in Russia itself within range of artillery.

In Vilkhivka, a shattered village east of Kharkiv, the thump of near constant artillery and swoosh of multiple rocket launchers could be heard from fighting at the front.

The Kremlin calls its actions in Ukraine a "special military operation" to demilitarise a neighbour threatening its security. It denies targeting civilians.

Ukraine says it poses no threat and that the deaths of thousands of civilians and destruction of towns and cities show that Russia is waging a war of conquest.

GAS SUPPLIES

Wednesday's move by Ukraine to cut off Russian gas supplies through territory held by Russian-backed separatists was the first time the conflict has directly disrupted shipments to Europe.

Gas flows from Russia's export monopoly Gazprom to Europe via Ukraine fell by a quarter after Kyiv said it was forced to halt all flows from one route, through the Sokhranovka transit point in southern Russia.