(Updates with grenade blast, paragraph 10)

By Matt Robinson

PRISTINA, Serbia, March 28 (Reuters) - The West and Russia on Wednesday reaffirmed a "shared sense of responsibility" for peace in Kosovo, Britain said, in response to warnings of unrest if Moscow blocks a U.N. plan to give the territory independence.

Western powers leading 16,500 troops in the breakaway Serbian province fear a revolt by the 90-percent ethnic Albanian majority if the U.N. Security Council fails to endorse the plan.

Senior diplomats of the six-power Contact Group steering Balkan diplomacy met on Wednesday in London as the U.N. Security Council prepares to open debate on Kosovo's future in April.

"The Contact Group remains united in its shared sense of responsibility to promote peace in Kosovo and in the region, despite any differences of perception," the British liaison office in Kosovo said in a statement.

The Contact Group comprises the United States, Britain, Germany, France, Italy and Russia.

All but Russia have endorsed the recommendations drafted by former Finnish President Martti Ahtisaari.

His blueprint offers Kosovo independence under European Union supervision, eight years since NATO bombs drove out Serb forces accused of atrocities in a 1998-99 war with Albanian separatist guerrillas. The United Nations took control.

Russia maintains a solution must be found that would be acceptable to both sides, something Ahtisaari says is impossible having mediated 13 months of fruitless Serb-Albanian dialogue.

Serbian Prime Minister Vojislav Kostunica said on Tuesday Russia would veto the plan at the U.N. Security Council, a move diplomats say would plunge Kosovo into chaos and almost certainly draw a unilateral declaration of independence.

As if to drive the point home, a hand grenade exploded late on Wednesday outside the home of a Kosovo Serb policeman in the flashpoint town of Mitrovica, a police source said. It was the third such blast in Mitrovica since Friday in one of the few mixed Serb-Albanian areas of the town. No one was hurt.

Moscow has avoided threatening the use of its veto, but has called for more talks, if necessary under a new mediator.

Washington says a new U.N. resolution could be adopted in April or May, but some European diplomats caution it might take longer to get the Russians on board.

An internal EU paper seen by Reuters warns of a possible upsurge in violence during the planned 120-day transition period from the U.N. mission (UNMIK). "It will be extremely important that UNMIK, while on its way out, will during this period still be capable to fulfil its mandate," it says. (Additional reporting by Mark John in Brussels and Branislav Krstic in Mitrovica)

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