A Pentagon watchdog is launching a probe into how the Department of Defense has addressed "Unidentified Aerial Phenomena" or UAP, after a string of UFO sightings in recent years that have been spotted by military aircraft. 

In a Monday memo to military and intelligence leaders, Randolph Stone, assistant inspector general for evaluations on space, intelligence, engineering and oversight, said the objective of the probe is to determine the extent to which the DoD has taken actions regarding Unidentified Aerial Phenomena (UAP).

"We may revise the objective as the evaluation proceeds, and we will consider suggestions from management for additional or revised objectives," he added.

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The Office of Inspector General typically investigates whistleblower complaints and allegations of wrongdoing, among other matters. 

It was not clear who decided to launch the probe or what investigators will specifically look for. 

A Pentagon watchdog is launching a probe into the actions taken by the Department of Defense after a series of UFO sightings in recent years.

A Pentagon watchdog is launching a probe into the actions taken by the Department of Defense after a series of UFO sightings in recent years. (Department of Defense)

The Pentagon created the Unidentified Aerial Phenomenon Task Force following several unexplained incidents observed by the military. It is tasked with detecting, analyzing and cataloging UAPs that could potentially pose a threat to U.S. national security.

In an interview with the New York Post, Luis Elizondo, the former head of the Pentagon's Advanced Aerospace Threat Identification Program, recently raised the possibility that so-called UFOs are actually "adversarial foreign technology that for several decades now has managed to leapfrog us."

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Monday's announcement comes as Congress awaits a report from the Pentagon and U.S. intelligence agencies about the presence of UFOs. Some government officials have accused the military and spy agencies of blocking or ignoring efforts to catalog instances of UAP, Politico reported. 

Last year, the Defense Department released three videos of Navy pilots encountering UFOs in 2004 and 2015.