Three videos posted online that have been described as being related to UFO sightings do indeed include footage of “unidentified aerial phenomena,” a U.S. Navy spokesman confirmed.

But as for specifics, spokesman Joseph Gradisher said the Navy doesn't know exactly what the objects are.

"The three videos (one from 2004 and two from 2015) show incursions into our military training ranges by unidentified aerial phenomena," Gradisher told NBC News in an emailed statement.

"The Navy has characterized the observed phenomena as unidentified," he said.

To the Stars Academy of Arts and Sciences, a group dedicated to pursuing research into UFOs and extraterrestrial life that was co-founded by rocker Tom DeLonge of Blink 182, helped bring attention to the videos. The three videos were posted by TTSA and The New York Times in December 2017 and March 2018, NBC New York reported.

The website The Black Vault last week first reported the Navy's "unidentified aerial phenomena" designation and said the three videos are commonly known as "FLIR1," "Gimbal" and "GoFast."

The video called FLIR1 shows an oblong-shaped object, which accelerates out of view from sensors. The group says that video is from 2004 and the "2004 Nimitz incident."

Gradisher did not name the videos in his emails, but said the video from the 2004 sighting is from an aircraft from the carrier USS Nimitz.

In the video called Gimbal, a crew member is heard saying "look at that thing" about an object that they said appeared to be going against the wind. One says they believed it was a drone.

The video called Go Fast, which the group says is from 2015, shows an object that appears to be over water and crews are heard asking "what the f--- is that?" and "what is that, man?"

To The Stars Academy of Arts & Science says online that U.S. military videos of “unidentified aerial phenomenon" have been through the declassification review process and approved for public release.

Gradisher disputed those assertions. He said the video from 2004 from the Nimitz was widely shared throughout the ship at the time and was posted online by a crew member in 2007. The online post came to the attention of Navy officials in 2009, but officials decided not to pursue the matter because of the time that had elapsed and the size of the crew at the time, which was around 5,000, he said.

The Navy "has no information" on how the other two videos were released into general circulation, Gradisher said. “These videos are copies of official Navy footage taken by Naval personnel conducting training missions in controlled military airspace," he said.

The New York Times reported in 2017 that the Pentagon’s Advanced Aerospace Threat Identification Program for years investigated reports of unidentified flying objects, but that the Defense Department said that program was shut down in 2012. What was described as a shadowy program was reported to have begun in 2007.

Gradisher said in emails that the larger issue about the three videos is what he called an increase “in the number of military training range incursions by unidentified aerial [phenomena],” and he said all such sightings are investigated.

"Any incursion into our training ranges by any aircraft or phenomena, identified or not identified, is problematic from both a safety and security concern," he said.

While the objects in the three videos in question are designated as unknown, Gradisher said that as inexpensive unmanned aerial systems — commonly called drones — become more prevalent, "sightings of this nature have increased in frequency."

While popular culture may refer to unexplained objects as UFOs, the phrase “unidentified aerial phenomena” was borrowed from the United Kingdom and describes “any aerial phenomenon that cannot immediately be identified," Gradisher said.

Seth Shostak, senior astronomer and institute fellow at the SETI Institute in Mountain View, California, said in an email Wednesday night that all that the Navy did with its confirmation of the videos and the “unidentified aerial phenomena” was confirm that the videos were authentic.

“The videos weren’t really being questioned. What IS being asked is ‘what the heck are these things?’” Shostak, a regular contributor to NBC News MACH, said in an email. “Now I think if the answer were easy, that would be known by now. But when I look at these things I see no reason to consider them good evidence for ‘alien visitation,’ which is what the public likes to think they are.”

He said that in some reported sightings of unidentified flying objects other explanations, like birds, seem plausible.