Iran said it had warned U.S. aircraft to keep away from military drills its holding over three days in a large maritime region reaching from the Persian Gulf to the northern Indian Ocean.

Military spokesman Commodore Shahram Irani said foreign manned and unmanned aircraft had been cautioned on Wednesday to avoid the exercises taking place over 2 million square kilometers of ocean, state-run Islamic Republic News Agency reported.

The area lies to the east of the Strait of Hormuz, a major choke point for oil shipments.

Iran and the U.S. are locked in a dispute over Tehran’s nuclear program and regional role. The Trump administration left the 2015 nuclear deal and reimposed sanctions two years ago, raising tensions that have on occasion sparked fears of another war in the region, including over attacks on Gulf shipping.

Irani said Iran’s military had witnessed increased activity by U.S. drones in the exercise area, and the aircraft had “changed their behavior” after receiving the warning, IRNA said.

The drills will involve warships, submarines, aircraft and a domestically produced drone, the Tasnim news agency said.

In a separate report, it said Iran would also join military exercises in southern Russia later this month, along with forces from China and several other countries.