A former US Pentagon insider has accused the US Government of ignoring evidence of unidentified flying objects (UFOs) following the release of new declassified Department of Defence (DoD) footage.

Key points: A new video purportedly shows US Air Force aircraft monitoring a UFO off the US Coast in 2015

A new video purportedly shows US Air Force aircraft monitoring a UFO off the US Coast in 2015 Former deputy assistant secretary of defence for intelligence, Chris Mellon, says reports remain "largely ignored and unevaluated" by the Pentagon

Former deputy assistant secretary of defence for intelligence, Chris Mellon, says reports remain "largely ignored and unevaluated" by the Pentagon The video emerged four months after the Pentagon confirmed the existence of a secret UFO program

The video, released on March 9, purportedly shows US Air Force aircraft monitoring a UFO off the United States east coast at an altitude of 7,500 metres in 2015.

The footage was made public by To The Stars Academy of Art and Science (TTSA), a research organisation founded in October 2017 by former Pentagon official Luis Elizondo, to conduct research into "exotic science and technologies".

An analysis of the video, published by TTSA, said the UFO showed no obvious wings or tails and was seen moving at a high speed "very low" above the ocean surface.

TTSA also said that there was no exhaust plume from the object, which would be visible on conventional aircraft filmed in the manner seen in the video.

What a typical F-16 flight would have looked like to the pilots on the monitors. ( Supplied: TTSA )

The video has emerged just four months after the DoD confirmed the existence of a secret $US22 million program to investigate UFOs which ran from 2007 to 2012.

The Pentagon shut down the program but backers claimed it remained in existence to investigate episodes brought to its attention by service members.

But Christopher Mellon, an adviser to TTSA and a former deputy assistant secretary of defence for intelligence, said credible "reports from different services and agencies remain largely ignored and unevaluated" by the Pentagon.

Writing in the Washington Post in response to the new footage released by TTSA, Mr Mellon criticised the lack of action in response to such incidents.

"The videos, along with observations by pilots and radar operators, appear to provide evidence of the existence of aircraft far superior to anything possessed by the United States or its allies," Mr Mellon wrote.

"Is it possible that … they might be evidence of some civilisation?

"We have no idea, because we aren't even seeking answers."

In the article, Mr Mellon describes a cultural stigma inside the Pentagon against anyone who pursues the idea that the UFOs are linked to extraterrestrial lifeforms.

"Nobody wants to be 'the alien guy' in the national security bureaucracy," Mr Mellon wrote.

"Nobody wants to be ridiculed or sidelined for drawing attention to the issue.

"This is true up and down the chain of command, and it is a serious and recurring impediment to progress."

The Pentagon admitted it ran a secret UFO investigation program for five years until 2012. ( AP: Charles Pharapak )

As a result, Mr Mellon claims the military does virtually nothing with the numerous reports of UFOs that soldiers make.

"There is no Pentagon process for synthesising all the observations the military is making. The current approach is equivalent to having the army conduct a submarine search without the navy," Mr Mellon said.

"What we lack above all is recognition that this issue warrants a serious collection and analysis effort."

The DoD has declined to comment on the latest video but in a statement last year said it took all threats to mankind seriously.

"The DoD takes seriously all threats and potential threats to our people, our assets and our mission, and takes action whenever credible information is developed," the Pentagon said in December.

Scientists have stressed that unexplained phenomena are not proof of interstellar visitors.