The Kremlin says President Vladimir Putin will seek binding guarantees precluding NATO’s expansion to Ukraine during a planned call with U.S. President Joe Biden.

Earlier Friday, the Ukrainian defense minister warned that Russia could invade his country next month.

Russia-West tensions have escalated with Ukraine and its Western backers becoming increasingly concerned that a Russian troop buildup near the Ukrainian border could signal Moscow’s intention to invade.

Speaking to reporters in Washington Biden said his administration was putting together “the most comprehensive and meaningful set of initiatives” to prevent any Russian escalation.

The U.S. has already threatened the Kremlin with the toughest sanctions yet if it launches an attack.