President Joe Biden told Ukrainian President Volodymyr Zelensky in a Sunday phone call that the U.S. “will respond decisively” should Russia invade Ukraine further, according to the White House. The reaffirmation of U.S. support comes amid an ongoing military crisis on the Ukraine-Russian border, as Russia’s heavy troop buildup on the fringes of its neighbor stokes fears of an impending invasion. White House press secretary Jen Psaki said in a statement following the call that Biden also reiterated his commitment to a policy of “nothing about you without you,” the diplomatic principle of U.S. negotiation on behalf of a European country only with that country’s input. Biden’s call with Zelensky comes ahead of security talks set to begin between Russian and U.S. officials on Jan. 9 in Geneva. Biden told reporters earlier this week that he had warned President Vladimir Putin that there would be a “heavy price to pay” should Russia continue to move against Ukraine, threatening heavy economic sanctions during their 50-minute Thursday phone call.