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, the 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.
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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.
2) Neutrality: Russia says it wants Ukraine to be a neutral country. Russia's chief negotiator Vladimir Medinsky says Ukraine has suggested it could be neutral like Austria or Sweden but with its own army. Kyiv has disputed that characterisation.
It is unclear how that neutrality might look so the devil will be in the detail. As the Soviet Union crumbled, Ukraine's parliament in its 1990 Declaration of State Sovereignty proclaimed its intention to be a permanently neutral state.
Medinsky said there were discussions about how big the Ukrainian army could be.
Putin said in February that he wanted written guarantees that Ukraine would never join the NATO military alliance. Ukrainian President Volodymyr Zelenskyy has said Ukraine would not become a NATO member soon because NATO members would not accept Ukraine.
Russia has also repeatedly raised concerns about Ukraine developing nuclear weapons. In the 1994 Budapest Memorandum, the United States, Russia and the United Kingdom gave Ukraine security assurances in exchange for Kyiv's adherence to the Treaty on the Non-Proliferation of Nuclear Weapons.
3) Russian rights: The status of the Russian language and Russian-speaking people in Ukraine is a major issue for Moscow. A law passed by Ukraine in 2019 granted special status to the Ukrainian language and made it mandatory for public sector workers.
The law obliges all citizens to know the Ukrainian language and makes it a mandatory requirement for civil servants, soldiers, doctors, and teachers.
4) "De-Nazification": Putin says Ukraine has allowed Nazi-like groups to commit "genocide" against Russian speaking communities in Ukraine.
The Azov Battalion, part of Ukraine's national guard, has been accused by Moscow of being a Nazi organisation that has terrorised Russian civilians and carried out war crimes.
Formed in 2014 from volunteers who fought against Russian-backed rebel regions, its founders have expressed extreme right-wing white supremacist and anti-Semitic views. The Azov Battalion did not reply to a request for comment.
Ukrainian presidential aides have repeatedly mentioned the role of Azov in the defence of the port city of Mariupol where it is based.
Ukraine dismisses such claims of genocide against Russian speakers. Zelenskyy says it is Russia that is behaving like the Nazis by visiting destruction on Ukrainian cities.
WHO IS TALKING AND HOW?
Talks on trying to find an end to the conflict began on Feb. 28, four days after Putin ordered troops into Ukraine. Some talks have been in person at the Belarusian border or in Belarus while others have taken place via video conference.
The Russian negotiating team is led by Russian presidential adviser Medinsky, a Russian who was born in Soviet Ukraine but who casts modern Ukraine as a "historical phantom" because "the so-called history of Ukraine is not simply inextricably linked to the thousand-year history of Rus/Russia/USSR but it is Russian history itself".
He said last week there had been some progress.
Turkey is trying to push the two sides together as is Israel.
Turkish Foreign Minister Mevlut Cavusoglu told Turkish daily Hurriyet that Russia and Ukraine were nearing agreement on "critical" issues and he was hopeful for a ceasefire if the two sides did not backtrack from progress achieved so far.
Zelenskyy called on Saturday for comprehensive peace talks with Moscow.
Russia says there will be no meeting between Putin and Zelenskiy until there is a deal to be agreed.
Ukraine's negotiating team is Defence Minister Oleksii Reznikov and presidential adviser Podolyak.
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