Washington says a Russian Su-27 clipped an MQ-9 the day before, leaving the drone uncontrollable and requiring it to be brought down in the Black Sea, while Moscow denies responsibility.

"This hazardous episode is a part of a pattern of aggressive, risky and unsafe actions by Russian pilots in international airspace," Austin said at the start of a meeting of countries supporting Ukraine's fight against invading Russian forces.

"Make no mistake, the United States will continue to fly and to operate wherever international law allows. And it is incumbent upon Russia to operate its military aircraft in a safe and professional manner," he added.

Russia's war in Ukraine has led to heightened fears of a direct confrontation between Moscow and the NATO alliance, which has been arming Kyiv to help it defend itself.

The United States uses MQ-9s for both surveillance and strikes and has long operated over the Black Sea, keeping an eye on Russian naval forces.

Several of the drones have been lost in recent years, including one that the US Central Command said was shot down over Yemen with a surface-to-air missile fired by Huthi rebels.