A US fighter jet has been shot down over Iran and search-and-rescue efforts have so far recovered one of two crew members who ejected, a US official told Reuters, in the first known incident of its kind in the nearly five-week-old war.

The Pentagon and US Central Command did not respond to requests for comment.

The prospect of a US pilot being alive and on the run inside Iran raises the stakes for the United States 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.

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.

William Goodhind, a forensic imagery analyst with Contested Ground, said images of the plane’s tail fin seen in photos posted on social media are consistent with those of an F-15E Strike Eagle, which carries two crew.

The governor of Kohgiluyeh and Boyer-Ahmad province said anyone who captured or killed the crew “would be specially commended,” Iran’s semi-official news agency Isna reported.

The incident follows threats by US President Donald Trump to bomb the country back to the “Stone Age,” including to attack Iran’s energy infrastructure and desalination plants, as he presses Tehran to end the war on US terms.

So far, 13 US military service members have been killed in the conflict and more than 300 have been wounded, according to the US Central Command. No US troops have been taken prisoner by Iran.

The US and Israeli war with Iran has spread across the Middle East, killing thousands of people and hitting the global economy with soaring energy prices that are fuelling fears of inflation in countries around the world.

The war is unpopular with Americans, with two-thirds believing the US should work to end its involvement in the conflict quickly, even if that means not achieving the goals set out by the Trump administration, a Reuters/Ipsos poll showed this week.