Iran has begun a three-day military exercise near the strategic Strait of Hormuz, according to state media, with the drill taking place at a time of heightened tensions with the United States.
Naval, air and ground forces were participating in the manoeuvres across a nearly two million-square-kilometre (772,200-square-mile) area off the Gulf of Oman on Thursday.
State television said Iranian submarines and drones had also been deployed for the exercise, dubbed Zolfaghar-99.
Admiral Habibollah Sayyari, commander of the drill, said the exercise was aimed at "improving readiness in confronting foreign threats and any possible invasion".
Meanwhile, the spokesman for the drill, Admiral Shahram Irani, told state television that the US had withdrawn drones from the area of the exercise after a warning from Iran.
Long-standing tensions between the US and Iran escalated in 2018 when President Donald Trump unilaterally withdrew Washington from a multinational accord that had lifted international sanctions off Tehran in return for the freezing of its nuclear programme.
Adopting a campaign of "maximum pressure", the Trump administration then reimposed crippling sanctions on the Iranian economy and has sought to extend a years-long United Nations arms embargo on Iran that is due to expire in October.
The two foes have come to the brink of direct confrontation twice since June 2019, when Iran shot down a US drone in the Gulf.
Fears of a full-blown military conflict deepened after Iran's most prominent general, Qassem Soleimani, was assassinated in a US drone strike near Baghdad airport on January 3.
Five days later, Iran retaliated by launching a wave of missiles at two bases in Iraq hosting US troops, causing no fatalities.
Tehran, which opposes the presence of US and other Western navies in the Gulf, holds annual naval war games in phases in the Strait of Hormuz, a key oil-trading route.
At another exercise in late July near the Strait of Hormuz, Iranian forces fired a missile from a helicopter targeting a replica of a US aircraft carrier.
