The Iranian army shot down an unidentified drone near the port of Bandar-e Mahshahr on the Gulf coast on Friday, Iran's semi-official ISNA news agency reported.
The unmanned aircraft was downed over Iranian territory with a domestically manufactured Mersad surface-to-air missile, said Tasnim news agency which is close to the ultra-conservatives.
Neither news agency gave any further details of the incident which comes amid soaring tensions between Tehran and Washington since President Donald Trump unilaterally abandoned a landmark 2015 nuclear deal last year and reimposed crippling sanctions.
Trump in June authorised a military strike after Iran shot down a US drone, only to call off the retaliation at the last moment.
Washington insists the aircraft was in international airspace, but Iran says it was over its territorial waters.
The crisis deepened with the September 14 attacks on Saudi energy giant Aramco's Abqaiq processing plant and Khurais oilfield which halved the kingdom's crude output.
Yemen's Iran-backed Huthi rebels claimed responsibility, but the US says the attacks involved cruise missiles from Iran and amounted to "an act of war".
Washington has responded with a military build-up in the Gulf and on Thursday launched an operation with its allies to protect navigation in Gulf waters.
Since May the United States has increased its 70,000-strong presence in the Middle East by 14,000 personnel, according to Pentagon figures, most of them deployed to the Gulf region.
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