Joe Biden and Vladimir Putin will face off in a high-stakes video call Tuesday, with the US president aiming to convince his Russian counterpart to refrain from attacking Ukraine. Washington and its European allies are uncertain if the tens of thousands of ground forces that Moscow has moved to Ukraine’s borders are a genuine invasion threat or a bluff by the Russian leader. The presidents — who met in person in Geneva this summer — will speak at 1500 GMT (18:00 pm Moscow time). “Our president is ready to convey his concerns to his American colleague, listen to his concerns and give appropriate explanations,” Kremlin spokesman Dmitry Peskov said Tuesday. “Russia has never planned to attack anyone,” he said. “But we have our own ‘red lines'”. Moscow — which annexed Kiev’s Crimea peninsula in 2014 and backs pro-Russia rebels in eastern Ukraine — has described Western accusations of an imminent invasion as “hysteria.” It has also spent weeks decrying US-led military exercises in the Black Sea and Putin wants a promise from the West that Ukraine will not join NATO. If he decides to attack Ukraine, Putin risks a coordinated Western response that could aim to cripple Russia’s economy. A senior Biden administration official said Monday that the US and its allies are prepared to punish Moscow with “substantial economic countermeasures” if it launches an attack. On the eve of his virtual meeting, Biden spoke with the leaders of France, Germany, Italy and Britain, with the Western powers expressing their “determination” that Ukraine’s sovereignty be respected. – Tensions ‘off the charts’ – The Kremlin said the conversation will take place in a “difficult period” when “the escalation of tensions in Europe is off the charts.” “This requires a personal discussion at the highest level,” Peskov said. In their first direct conversation since July, the two presidents will have to negotiate a history of mutual suspicion. Both want to put on a show of strength, which could leave little room for compromise during the talk. Biden said Friday he would make it “very, very difficult” for Russia to launch an invasion. A senior official said that any Russian military action against Ukraine would be met with harsh economic penalties and a buildup of US forces in Eastern Europe. But the official stopped short of threatening direct intervention of American military force. Such talk, the official added, “would be precipitous conflict saber-rattling, and we’d prefer to keep those communications with the Russians private.” Biden will make clear that there “will be genuine and meaningful and enduring costs to choosing to go forward should (Russia) choose to go forward with a military escalation,” the official said. – ‘Window of opportunity’ – Biden and Putin have a full list of topics to discuss, from mutual talks on reducing strategic and nuclear threats, to the rise in cyberattacks that Washington says Moscow encourages, to persuading Iran to halt its nuclear program. But Russia’s massing of troops to the Ukraine border region — estimated by Kiev at 100,000 — has forced the virtual summit to focus on that one issue. Putin has said Russia was “taking adequate military-technical measures,” claiming NATO military infrastructure was moving “close” to Russia’s borders. He said Moscow seeks “legal guarantees” that Ukraine will not become a part of NATO, the transatlantic alliance created to confront the former Soviet Union. US State Department spokesman Ned Price indicated Monday that Washington wants Russia to back down and return to the 2015 Minsk Agreement aimed at halting the fighting inside Ukraine. “We believe there is an opportunity, a window before us to resolve this diplomatically,” Price said. – Zelensky to the front – Ukraine’s President Volodymyr Zelensky on Monday visited troops fighting pro-Moscow separatists in the country’s east on Monday. The conflict has claimed over 13,000 lives. “Thank you for protecting the sovereignty and territorial integrity of Ukraine,” Zelensky, wearing a military helmet and body armour, told the soldiers according to a statement released by Kiev. On Monday he spoke with US Secretary of State Antony Blinken, writing on Twitter after that he was “grateful” to the US and allies for supporting Ukraine.