The head of Nasa has said he believes accounts of UFOs, as he commissioned an eight-month inquiry to investigate hundreds of unexplained sightings.

Bill Nelson, the former space shuttle astronaut and US senator, said he had personally talked to two Navy pilots who saw numerous flying objects in 2004, and had turned over the investigation to Nasa’s top scientist.

“We're taking this very seriously,” he told a briefing of science journalists.

“I've talked to the Navy pilots that know that they saw something back in 2004. They tracked it on their radar off the Southern California coast, over the Pacific.

“Since then hundreds of objects have been spotted and a couple of them were explained, they may be balloons, but most of them are unexplained.

“So I’ve asked Nasa, and it will be announced within a few days, to approach this subject from a scientific standpoint, since we are a scientific research organisation. In about eight months, they’re going to report.”

Asked whether he thought the sightings could be enemy aircraft, the Nasa administrator added: “Do I think it's an enemy? I hope it isn't, because the Navy pilots would describe it as: 'It's here and then it's over there. With no time in between.'

“And so my simple answer is I don't know. And that's why I've asked our scientists to see if they've got any explanation.”

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