Despite lengthy weekend talks between Moscow and Washington, some airlines have canceled or redirected flights to Ukraine amid fears from the West that a Russian invasion is imminent.

President Joe Biden said in an hour-long call with Russian President Vladimir Putin on Saturday that an invasion of Ukraine would result in widespread human suffering and that the West was committed to diplomacy to resolve the crisis but was also prepared for other scenarios, according to the White House. It made no attempt to imply that the appeal lessened the possibility of a European conflict.

Biden will meet with Zelenskyy later Sunday, according to the White House.

Jake Sullivan, Biden’s national security adviser, said on Friday that US data indicates a Russian invasion may start within days. President Volodymyr Zelenskyy of Ukraine has downplayed invasion fears, encouraging the population to remain calm.

Russia has amassed around 100,000 troops near its border and has sent troops to drills in Belarus, despite denying that it intends to invade Ukraine. According to US authorities, Russia’s military buildup has reached the stage where it may invade at any time.

After the plane’s Irish lessor claimed it was barring flights in Ukrainian airspace, the Ukrainian charter airline SkyUp said its flight from Madeira, Portugal, to Kyiv was diverted to Chisinau, Moldova.

Ukraine has not blocked its airspace, according to Ukrainian presidential spokesman Serhii Nykyforov. According to a statement from the Infrastructure Ministry, several carriers are having difficulties as a result of insurance market changes.

Russia is requesting that the West exclude former Soviet republics from NATO membership. It also wants NATO to stop stationing weapons near its border and withdraw alliance forces from Eastern Europe, demands that the West has firmly rejected.

Since 2014, when Ukraine’s Kremlin-friendly president was forced from office by a popular uprising, Russia and Ukraine have been at odds. Moscow retaliated by annexing the Crimean Peninsula and then supporting a separatist insurgency in eastern Ukraine, where over 14,000 people have been murdered in conflict.