Canadian Prime Minister Justin Trudeau’s shocking allegations that India orchestrated the murder of a separatist leader leaves U.S. President Joe Biden caught between one of Washington's closest allies and an increasingly important partner in countering China.

Indian leader Narendra Modi’s government on Tuesday denied that it had anything to do with the slaying of a prominent Sikh leader in Canada, calling the allegation "absurd.” Both nations expelled one of the other’s diplomats, and that’s before Canada has made any evidence public.

The White House reacted cautiously, with National Security Council spokesperson Adrienne Watson saying the administration was "deeply concerned” and called on India to cooperate with the Canadian investigation. A U.S. official acknowledged the allegations pose a problem for Biden, who just left India with relations seemingly on track.