US President Joe Biden spoke with Ukraine’s President Volodymyr Zelenskiy on Sunday to discuss Russia’s troop buildup near its Ukraine border and vowed Washington and its allies would “respond decisively” if Russia invades Ukraine, according to a White House statement. Russia currently has amassed some 100,000 troops along its border with Ukraine, according to analysts.

The United States and its Western allies have an upcoming series of diplomatic meetings to address the tension along Russia’s border with Ukraine. Biden and Zelenskiy discussed preparations for the upcoming meetings during Sunday’s phone call.

“President Biden made clear that the United States and its allies and partners will respond decisively if Russia further invades Ukraine,” White House spokesperson Jen Psaki said in a statement following the call between Biden and Zelenskiy. Moreover, the statement from the White House said, “President Biden underscored the commitment of the United States and its allies and partners to the principle of ‘nothing about [Ukraine] without [Ukraine].’” 

On Twitter, Zelenskiy wrote that he and Biden discussed joint actions for keeping peace and preventing escalation. Zelenskiy tweeted that the joint actions of Ukraine, the United States “and partners in keeping peace in Europe, preventing further escalation, reforms, deoligarchization were discussed. We appreciate the unwavering support of Ukraine.”

Biden spoke with Putin about the issue by phone on Thursday. According to a White House statement released after the call, Biden “made clear that the United States and its allies and partners will respond decisively if Russia further invades Ukraine.” The White House statement did not clarify what such a response would entail, but according to a Kremlin statement on the same call, “Biden emphasized… that Washington had no intention of deploying offensive strike weapons in Ukraine,” but mentioned the threat of “large-scale” sanctions.