Moscow warned Washington on Wednesday to keep well away from its air space, after a U.S. drone intercepted by Russian jets crashed into the Black Sea, the first known direct confrontation between the superpowers since Russia invaded Ukraine.

Washington and Moscow traded blame for the incident, which took place in international air space near territory Russia claims to have annexed from Ukraine. Moscow called it proof that the United States was directly participating in the war; Washington called it an act of Russian recklessness.