The Pentagon has officially released three short grainy videos showing "unidentified aerial phenomena", report several media including CNN and The Guardian.
The videos, previously released by a private company, show what appear to be unidentified flying objects rapidly moving while being recorded by infrared cameras.
Two of the videos contain service members reacting in awe at how quickly the objects are moving. One voice speculates that it could be a drone.
The Pentagon said it released the footage to "to clear up any misconceptions by the public on whether or not the footage that has been circulating was real or whether or not there is more to the videos," reports The Guardian quoting a statement on the US Department of Defense website.
"After a thorough review, the department has determined that the authorised release of these unclassified videos does not reveal any sensitive capabilities or systems, and does not impinge on any subsequent investigations of military air space incursions by unidentified aerial phenomena," the statement said.
The US Navy previously acknowledged the veracity of the videos in September last year.
The Navy now has formal guidelines for how its pilots can report when they believe they have seen possible UFOs, according to CNN.
The Navy videos were first released between December 2017 and March 2018 by To The Stars Academy of Arts & Sciences, a company co-founded by former Blink-182 musician Tom DeLonge, that says it studies information about unidentified aerial phenomena.
In 2017, one of the pilots who saw one of the unidentified objects in 2004 told CNN that it moved in ways he couldn't explain.
"As I got close to it ... it rapidly accelerated to the south, and disappeared in less than two seconds," said retired US Navy pilot David Fravor. "This was extremely abrupt, like a ping pong ball, bouncing off a wall. It would hit and go the other way."
The Pentagon has previously studied recordings of aerial encounters with unknown objects as part of a since-shuttered classified programme that was launched at the behest of former Senator Harry Reid of Nevada. The programme was launched in 2007 and ended in 2012, according to the Pentagon, because they assessed that there were higher priorities that needed funding.
Nevertheless, Luis Elizondo, the former head of the classified programme, told CNN in 2017 that he personally believes "there is very compelling evidence that we may not be alone."
"These aircraft -- we'll call them aircraft -- are displaying characteristics that are not currently within the US inventory nor in any foreign inventory that we are aware of," Elizondo said of objects they researched. He says he resigned from the Defense Department in 2017 in protest over the secrecy surrounding the programme and the internal opposition to funding it.
Reid tweeted on Monday that he was "glad" the Pentagon officially released the videos, but that "it only scratches the surface of research and materials available. The US needs to take a serious, scientific look at this and any potential national security implications."