ABUJA, Nigeria (AP) — The United States and European Union are expressing concern after Nigeria's president suspended the country's chief justice three weeks before the presidential election, with the U.S. warning it could "cast a pall" over the vote.

President Muhammadu Buhari set off an uproar on Friday by announcing the suspension over graft allegations. The chief justice would play a key role in any legal challenge to the election.

The U.S. on Saturday says Buhari acted "without the support of the legislative branch" and notes widespread criticism that the move was unconstitutional. It urges Nigerian authorities to quickly resolve the crisis that could undermine the credibility of the Feb. 16 vote.

The EU election observer mission calls on all parties to "respond calmly." Some Nigerian elections have been marked by violence.