SECOND US warplane 'shot down in Persian Gulf' as Americans scramble to rescue missing pilot

Iran's air defence system targeted an "enemy" A-10 aircraft in southern waters near the Hormuz Strait, the nation's state media said on Friday.

The Fairchild Republic A-10 Thunderbolt II, more commonly known as a "Warthog", attack plane went down near the Strait of Hormuz, with officials providing scant details about the crash, including how and where it happened.

This comes as another US fighter jet was downed over Iran earlier today, with President Donald Trump telling reporters that this won't impact negotiations with Iran.

White House Press Secretary Karoline Leavitt said the President had been briefed, without confirming any details of the incident.

Iranian officials called on civilians to be on the lookout for survivors and have flooded social media with images that purport to show wreckage from the aircraft.

Two US officials said the aircraft was an F-15E fighter jet, which has two seats: one for a pilot and the second for a weapons systems officer.

It was unclear which of the two was recovered, and the US official who confirmed the recovery did not offer any details on how it took place.

The prospect of a US pilot being alive and on the run inside Iran raises the stakes for Washington in a conflict that, according to opinion polls, has struggled to win popular support among Americans.

It also presents a challenge to the US military, which faces the twin goals of trying to save the life of an American behind enemy lines while safeguarding anyone involved in perilous rescue missions.

The incident comes over a week after President Trump said in the Oval Office that Iran's military had been defeated to the point that "we literally have planes flying over Tehran and other parts of their country. They can't do a thing about it."

US air crews undergo training for what to do if they go down behind enemy lines, called Survival, Evasion, Resistance and Escape training, or SERE, but few airmen are fluent in Persian and staying undetected while seeking rescue will be a challenge.

An unnamed source told Iran's semi-official Fars news agency on Friday that Tehran had rejected a US proposal for a 48-hour ceasefire.

The source said the proposal was made on Wednesday through another country, which was not named. There was no immediate comment or confirmation from the US.

As of last week, the US could only determine with certainty that it had destroyed about one-third of Iran's missile arsenal.

The status of about another third was less clear but bombings likely damaged, destroyed or buried those missiles in underground tunnels and bunkers, sources told Reuters.