(Bloomberg) — The U.S. said intelligence indicates Russia may attack Ukraine before the Olympics end on Feb. 20. Russia has said it has no intention of invading. Russia pushed back after NATO and the European Union said they’d only provide a collective response to its proposals on a regional security framework. Moscow had been seeking individual replies from each member nation of the EU. Western allies are seeking to show unity in the face of Russia’s military buildup near the Ukraine border, bolstering NATO’s eastern flank with added troops and threatening joint sanctions against Moscow if it were to invade Ukraine. U.S. President Joe Biden said conditions in the region could “go crazy quickly” as he urged Americans to leave Ukraine, and he held a call Friday with other leaders to discuss the tensions. Russia and Belarus are holding their largest joint military exercises in years through Feb. 20 near Ukraine’s border as well as those of NATO members Poland and Lithuania. The top U.S. military official spoke with his Belarusian counterpart to avoid a “miscalculation” around the drills. Russia Starts Major Military Drills in Belarus as NATO WatchesRussia and Europe Are Vital to Each Other When It Comes to OilWhat we know so far about potential U.S.-EU sanctions on RussiaWhere Military Forces Are Assembling Around Russia and UkraineEU to Send Russia Joint Security Reply, Snubbing Lavrov Demand The Pentagon is sending 3,000 more troops from the U.S. to Poland, according to a U.S. defense official, as part of the effort to bolster the American and NATO presence in Europe as tensions with Russia build over Ukraine. U.S. officials have said the troops are there for defensive purposes only and wouldn’t go into Ukraine. National Security Adviser Jake Sullivan said the U.S. believes Russian President Vladimir Putin could order an attack on Ukraine before the Olympics end on Feb. 20. “We continue to see signs of Russian escalation, including new forces arriving at the Ukrainian border,” Sullivan told reporters at the White House. “I will not comment on the details of our intelligence information, but I do want to be clear, it could begin during the Olympics despite a lot of speculation that it will only happen after the Olympics.” The actions by Russia could include causing a provocation in the Donbas region, where Ukraine’s military has been fighting for years against separatists backed by Moscow, or attacking the country’s capital, Kyiv, officials familiar with the matter said. They said any action could start as soon as Tuesday. He said Americans in Ukraine should leave “as soon as possible and in any event in the next 24 to 48 hours.” U.K. Defense Secretary Ben Wallace said he received fresh assurances Russia won’t invade Ukraine, having held talks Friday with Defense Minister Sergei Shoigu and Chief of the Russian General Staff Valery Gerasimov in Moscow. Still, Russian forces have the capability to attack Ukraine “at any time,” he told reporters. The talks with Shoigu were constructive and frank, Wallace said. “He is a professional, he is a very experienced minister, as is General Gerasimov. And when they say to me they are not going to invade Ukraine we will take that seriously. But as I have also said, we will look at the actions that accompany it.”