NASA is launching a further investigation into UFO sightings. The agency's chief says it can't rule out the possibility that sightings are of alien origin.

• NASA's new chief is launching an investigation to further study UFOs.
• There is no evidence that UFO sightings are of alien origin, but NASA is not ruling it out.
• "The bottom line is, we want to know," the chief told CNN.

NASA's new chief, Bill Nelson, is setting up an investigation to further study the existence of unidentified flying objects within his first month in office, CNN Business reports.

In an interview with the news outlet, Nelson said it's still a mystery to everyone - even those at the top of the space agency - what exactly the high-speed flying objects detected by US Navy personnel are.

Nelson said he does not believe that UFOs point to evidence of extraterrestrials visiting Earth. "I think I would know" if that were the situation, he said. But he accepted it would be hasty to rule that out as a possibility.

"We don't know if it's extraterrestrial. We don't know if it's an enemy. We don't know if it's an optical phenomenon," Nelson said. "We don't think [it's an optical phenomenon] because of the characteristics that those Navy jet pilots described ... And so the bottom line is, we want to know."

While no formal task force has been arranged yet, Nelson wants researchers to investigate the subject in depth.

The chief's comments mirror a Pentagon report, which says there is no evidence that UFOs spotted by US Navy pilots are of alien origin - but so little is known about them that it can't be ruled out, as reported by The New York Times.

One possible explanation the report will propose is that UFOs are advanced technology from other countries, The Times reported.

"There's not really a lot of data and...scientists should be free to follow these leads, and it shouldn't be stigmatized," Jackie McGuinness, a NASA press secretary, told CNN.