Russian President Vladimir Putin speeches during the Valdai Discussion Club's plenary meeting, on October,21,2021, in Sochi, Russia. Mikhail Svetlov | Getty Images News | Getty Images U.S. President Joe Biden is expected to give Russian President Vladimir Putin a stark warning against attacking Ukraine during a video call Tuesday, but experts say time is running out for the U.S. to prevent further hostilities between the neighboring countries. The call comes amid fears that Russia is planning on launching some form of military action against Ukraine following Russian military troop movements on the border and increasingly aggressive rhetoric towards Kiev from Moscow. For his part, Putin said on Nov. 30 that Russia was concerned about military exercises in Ukraine being carried out near the border, saying these posed a threat to Moscow. He has insisted that Russia is free to move troops around its own territory and has denied claims that the country could be preparing to invade Ukraine, calling such notions "alarmist." Close followers of Russian politics are not convinced that Russia's intentions toward Ukraine — which was a part of the Soviet Union until its dissolution in 1991 — are benign, however. Many experts (and Ukrainian leaders) believe that Putin — who said in 2005 that the break up of the union was "the greatest geopolitical catastrophe of the century" — harbors a desire to rebuild the Soviet empire, with Russia often seeking to extend, or impose, its influence on former Soviet republics like Belarus and Ukraine. Russia opposes Ukraine's aspirations to join NATO, and its neighbor, the EU. No compromise? Experts are also unconvinced that Biden, and allied nations in Europe, can find a compromise with Putin, warning that the window of opportunity to find a peaceful resolution to growing tensions between Russia, Ukraine and the wider West is closing. Russia expert Timothy Ash, a senior emerging markets sovereign strategist at BlueBay Asset Management, said the Putin-Biden call would likely be "very difficult" and that it was "hard to see where the compromises will come from." "Putin wants security guarantees on no further NATO enlargement, non-aligned status for Ukraine and limitations on Ukraine's rearmament and NATO troop presences in Ukraine. Biden cannot give these, and Ukraine would never agree — unless under extreme duress," Ash said in a note Monday evening. "Biden will use the stick of sanctions and the carrot of more talks to try and buy time for Ukraine to continue to build its defences. [The] question is, is Putin prepared to wait?" Ash added that Putin may well be thinking that now is the best time to enforce his will on Ukraine and the West. What Russia wants There have been reports of an increase in Russian troops on Ukraine's border for weeks, movements which have led NATO's Secretary General Jens Stoltenberg to warn that NATO members should prepare for the worst when it comes to Russia and Ukraine. "You can discuss whether the likelihood for an incursion is 20% or 80%, it doesn't matter. We need to be prepared for the worst," Stoltenberg told reporters on Nov.30 after a meeting of NATO foreign ministers in Riga, Latvia. "There is no certainty, no cl . . . read the full article here.