UFOs may be fodder for comedians and science fiction, but there was no joking on Monday when a group of pilots and officials demanded the US government reopen an investigation into unidentified flying objects.

The 19 former pilots and government officials, who say they have seen UFOs themselves or been involved in probes of strange flying objects, told reporters their questions can no longer be dismissed more than 30 years after the US case was closed.

"We want the US government to stop perpetuating the myth that all UFOs can be explained away in down-to-earth, conventional terms," said Fife Symington, former governor of Arizona and air force pilot who says he saw a UFO himself in 1997.

"Instead our country needs to reopen its official investigation that it shut down in 1969," Symington told a news conference.

Symington read an appeal on behalf of the group of who came to Washington to recount their sightings of UFOs.

"We believe that for reasons of both national security and flight safety, every country should make an effort to identify any object in its airspace," the statement said.

The group included a retired pilot from Air France who said he saw an enormous flying disc during a flight from Nice to London in 1994, an Iranian pilot who tried in vain to fire on a UFO in 1976 and a former US official from the Federal Aviation Administration (FAA) who claims a probe into a UFO seen over Alaska in 1987 was squelched.

"'Who believes in UFOs?' is the kind of attitude of the FAA all the time," said ex-FAA official John Callahan.

"However, when I asked the CIA person: 'What do you think it was?,' he responded: 'a UFO.'" When he suggested the government tell Americans about a UFO, the CIA official allegedly told him: "'No way, if we were to tell the American public there are UFOs they would panic.'"

The subject of UFOs came up in a recent debate among presidential candidates, with Democrat Dennis Kucinich saying he saw a UFO.

Sceptics say UFO sightings are merely aircraft or meteors re-entering the Earth's atmosphere.

The Air Force investigated 12,618 UFO reports from 1947 to 1969 in what was known as Project Blue Book. Investigators concluded that the incidents posed no threat and there was no evidence of space aliens or a super technology in operation.

"Since the termination of Project Blue Book, nothing has occurred that would support a resumption of UFO investigations," the Air Force said on its website. - Agencies