Armed tribal groups in Iran's Kohgiluyeh and Boyer-Ahmad province have fanned out across mountains and plains searching for the pilot of a US fighter jet Iran claims to have shot down, as American forces launched what appears to be a large-scale search and rescue operation, Tasnim News Agency reported on April 3.

Tasnim said the pilot ejected after the jet was hit by IRGC air defences and landed inside Iranian territory. Local sources said Washington was attempting to extract the pilot before Iranian forces could reach him.

Iranian state media correspondents across several provinces reported that US forces had deployed multiple Black Hawk helicopters, a C-130 Hercules transport aircraft and surveillance drones to search for the downed aviator.

The agencies said the search area was unusually wide, suggesting US forces did not have a precise fix on the pilot's location despite GPS tracking systems typically carried by combat aircrew.

In response to the missing pilot, an IRR100bn reward has been offered by merchants and guilds from the Kohgiluyeh and Boyer-Ahmad province Chamber of Commerce as the hunt continues. 

Separately, reports circulated that a US Black Hawk UH-60 helicopter had been shot down near the Iranian border during the search operation, according to IRGC media channels. The claims could not be independently verified by IntelliNews.

Tribesmen and villagers in Kohgiluyeh and Boyer-Ahmad, a rugged mountainous province in southwestern Iran, took up personal weapons and began patrolling their areas after reports of possible US helicopter activity in the region's airspace.

The incident, if confirmed, would represent the most significant US combat loss of the war. The Pentagon's most recent casualty count put losses at 13 killed and 348 wounded since February 28. The loss of a manned fighter jet and a potential rescue operation deep inside Iranian territory would mark a dangerous new phase in the conflict.

Tasnim earlier published images of wreckage it said belonged to the downed aircraft, identifying it from tail markings as an F-15 from the US 48th Fighter Wing based at RAF Lakenheath in England.

UPDATED: 15:00 UTC