The US Navy destroyed an Iranian drone on Thursday after it refused to back down, President Donald Trump says.
He said the USS Boxer downed the drone over the Strait of Hormuz - a strategic sea passage in the Gulf - after it came within 1,000 yards (914m) of the ship.
Iran said it had no information about losing a drone. In June, Iran shot down a US military drone in the area.
Iran has been blamed by the US for attacks on tankers which have happened in the world's key shipping area since May. Tehran denies all the accusations.
The recent incidents have triggered fears of a military conflict in the region.
Russia's unmanned Luna-25 spacecraft has crashed into the Moon after spinning out of control, officials say.
Donald Trump has confirmed that he will not take part in Republican presidential debates with his rivals in the race for the White House.