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EXPLAINER-Talks on Ukraine: peace deal or more Russian war?

LONDON, March 22 (Reuters) - Russia and Ukraine are talking about a peace deal while their soldiers kill each other after the Feb. 24 Russian invasion but the question of territory could sink any chance of an agreement to end the war.

Turkey, which is trying to mediate, has said the two sides are nearing agreement on critical issues. Britain has warned that President Vladimir Putin could be using peace talks as a smokescreen to regroup Russian forces.

Putin says the "special military operation" in Ukraine is necessary because the United States was using Ukraine to threaten Russia and Russia had to defend against the "genocide" of Russian-speaking people by Ukraine.

Ukraine says it is fighting for its existence against a Russian imperial-style land grab and that Putin's claims of genocide are nonsense.

The West has imposed sweeping sanctions on Russia that the Kremlin says amount to a declaration of economic war by the United States and its allies. China has called for calm.

WHAT ARE THE MAIN ISSUES?

1) Territory: This is the toughest part of the talks.

Russia annexed Crimea in 2014 and on Feb. 21 it recognised two Russian-backed rebel regions of eastern Ukraine as independent states.

Since the invasion, Russian forces have taken control of a swathe of territory across Ukraine's southern flank north of Crimea, territory around the rebel regions and territory to the east and west of Kyiv.

Russia has at least another 170,000 square kilometres of territory - an area about the size of Tunisia or the U.S. state of North Dakota - under its control.

Ukraine has said it will never recognise Russia's control over Crimea, the independence of the Russian-backed rebel regions or the vast additional territory taken by Russia.

"Our positions are unchanged," Ukrainian negotiator Mykhailo Podolyak said. He has said Ukraine insists on a ceasefire, the withdrawal of Russian troops and strong security guarantees.

Ukrainian officials say they will not accept the annexation of its territory or recognise the Russian-backed rebel regions of Luhansk and Donetsk.

Recognition of what amounts to effective Russian sovereignty over up to a third of its territory would be difficult for any Ukrainian leader.

For Moscow, Ukrainian recognition of Russian control of Crimea, the rebel regions and probably the swathe of land north of Crimea which gives it a land bridge to Crimea and control over drinking water supplies for the peninsula would be essential.

The territory along the southern flank of Ukraine is of particular interest to Russia as it was added to Russia in 1783 by Russian Empress Catherine the Great after the defeat of the Ottoman Empire.