"An Iranian army air force jet crashed into the Oman Sea Monday," IRNA said. "The plane, a Phantom, crashed into the waters near the (Iranian) port city of Konarak at 12:45 (0915 GMT)."
The semi-official Fars news agency said the fate of the pilot and the cause of the crash were still unknown.
During the pro-Western rule of Shah Reza Pahlavi, Iran's air force was considered the best-equipped in the region and operated some of America's most capable aircraft.
But following the installation of an Islamist regime in 1979, relations quickly soured and resulted in a U.S. arms embargo that remains to this day.
Left without spare parts during the 1980-1988 Iran-Iraq war, Iran's Air Force had to keep its planes in the air by cannibalizing other jets.
Although Iran has purchased an unspecified number of Russian-made Sukhoi fighter jets in the past two decades, experts agree that the bulk of the Iranian air force is still made up of Vietnam War-era F-14s, F-4 Phantoms and F-5s.
Iran, seeking to bolster its air defenses amid rising tensions over its nuclear program, has turned to Russia and China for the warplanes needed to replace its obsolete U.S. jets.
Both Moscow and Beijing refuse to comment on reports in the Israeli and Russian media, along with Western aviation publications, that Iran aims to order Russian Sukhoi Su-30 and Chinese Chengdu J-10 combat aircraft.
More recently, Iran has tried to develop its own indigenous manufacturing capability. The Saegeh (Thunderbolt) light fighter, which appears based on the old American F-5, has recently come off the production line.