Officials from Russia, and the United States and its NATO allies, are meeting this week for negotiations on Moscow's demand for Western security guarantees and the West's concerns about a recent buildup of Russian troops near Ukraine.
Russian and US negotiators have a round of talks scheduled in Geneva on Monday that will be followed by Russia-NATO talks in Brussels and a meeting in Vienna of the Organisation for Security and Cooperation in Europe over the course of the week.
Here is a look at the agenda of the security talks and the main issues of contention:
Russian invasion fears
The amassing of Russian troops and equipment near Ukraine's border has caused worries in Kyiv and in the West that Moscow could be planning to launch an invasion.
Moscow has denied such an intention and in turn accused Ukrainian authorities of planning an offensive to reclaim control over territories in eastern Ukraine held by Russia-backed separatists - allegations Ukraine has rejected.
US President Joe Biden twice discussed the Russian troop buildup with Russian President Vladimir Putin last month, warning that Moscow would face “severe consequences”, including unprecedented economic and financial sanctions, if it attacked its neighbour.
Russia annexed Ukraine's Crimean Peninsula in 2014 and has backed the separatist rebellion that started the same year in the country's east, where more than seven years of fighting has killed over 14,000 people. The West has responded with sanctions that have battered the Russian economy but failed to persuade Moscow to change course.
Russia's security demands
Putin has described the possibility of Ukraine joining NATO and the alliance deploying weapons there as a “red line” for Moscow. The Kremlin demanded that Washington and its allies make a binding pledge excluding NATO's expansion to Ukraine, Georgia or any other ex-Soviet nations.
Moscow has also demanded that the US and its allies make a commitment not to deploy weapons or conduct any military activities in Ukraine and other ex-Soviet nations.
The Kremlin has presented a draft Russia-US security treaty and a blueprint for a Russia-NATO agreement as a starting point for this week's negotiations. They would oblige the alliance not to station any troops in areas where they weren't present in 1997 -- before NATO moved to incorporate former Soviet bloc countries and ex-Soviet republics.
Moscow's proposals also suggest a freeze on patrols by Russian and US naval ships and bombers near each other's frontiers. In addition, they call for efforts to reduce the risk of incidents involving Russia and NATO warships and aircraft, primarily in the Baltic and the Black Seas; a reduction in the scope of military drills; greater transparency and other confidence-building measures.
US and NATO reaction
The US and its allies have roundly rejected the demand for NATO not to admit Ukraine or any other new members, emphasising that a key alliance principle is that membership is open to any qualifying country and no outsiders have veto power.
While Ukraine and Georgia aren't yet ready for NATO membership and have little prospect of being invited to join soon, the Western allies insist that NATO's doors must remain open to them. In 2008, NATO promised to eventually embrace the two nations, although it hasn't offered them a specific road map to membership.
Even though the allies firmly rejected a halt to NATO's expansion as a non-starter, Washington and NATO say they are ready to discuss arms control, confidence-building measures, greater transparency and risk reduction if Russia takes a constructive stance.
US officials said they are open to discussions on curtailing possible future deployments of offensive missiles in Ukraine and putting limits on American and NATO military exercises in Eastern Europe if Russia is willing to back off on Ukraine.
At the same time, the White House has urged Russia to help create a positive environment for the upcoming talks by pulling back its troops from areas near Ukraine. Moscow has dismissed the suggestion, saying it can deploy its forces wherever it deems necessary on its own territory and describing the buildup as a response to “hostile” moves by NATO.
Time limits
Putin has called the negotiations with the US a “positive” move but said he wants quick results, warning the West against trying to drown Russia's demands in “idle talk”.
Asked during a news conference last month if he could guarantee that Russia won't invade Ukraine, Putin responded angrily and said the West “must give us guarantees and give them immediately, now”.
Deputy Foreign Minister Sergei Ryabkov, who heads the Russian delegation at the security talks, described the demand for guarantees that NATO won't expand to Ukraine and other ex-Soviet nations as “absolutely essential” and warned that the US refusal to discuss it would make further talks senseless.
“We are going there not with a hand outstretched but with a precisely formulated task that we need to solve on conditions that we formulated,” Ryabkov said. He warned that Russia wouldn't make any concessions under threats and pressure and noted that the talks may end after the first round if the US and its allies are uncooperative
The Kremlin's blunt demands combined with a push for quick results have fuelled US suspicions that Moscow could make unrealistic requests just to see the talks collapse and then use it as a pretext for aggressive action. Russian diplomats have repudiated the claim.
Military-technical options
While Moscow has denied planning to attack Ukraine, Putin has warned that he would be forced to take unspecified “military-technical measures” if the West stonewalled on his security demands.
He didn't elaborate beyond saying the Russian response in that scenario “could be diverse” and “will depend on what proposals our military experts submit to me”.
Kremlin foreign policy adviser Yuri Ushakov said Putin had told Biden that Russia would act just as if the US would have acted if it saw offensive weapons deployed next to its borders.
Putin has noted that the new Zircon hypersonic cruise missile could give Russia a previously unseen precision strike potential if fitted to warships deployed to neutral waters. The launch of a salvo of Zircons in late December heralded the completion of tests for the new weapon, which Putin said flies at nine times the speed of sound to a range of more than 1,000 km (620 miles).
While voicing concern that NATO could potentially use Ukrainian territory for the deployment of missiles capable of reaching Moscow in just five minutes, Putin noted that Zircon would give Russia a similar capability.
“It would also need just five minutes to reach those who issue orders,” Putin said.