The Pentagon is tracking more and more UFO incidents but has yet to come across any evidence of alien activity, a Defense Department official told Congress on Wednesday.

Sean Kirkpatrick, director of the All-Domain Anomaly Resolution Office, testified that the Pentgaon is currently tracking some 650 instances of UFO sightings. Kirkpatrick made the statement during a Wednesday hearing before the Senate Armed Services Committee.

Kirkpatrick testified that many of the cases that reach his office are difficult to ever close, given a lack of verifiable information. As a result, only a "handful" of cases have been formally closed, he told lawmakers.

"I will not close a case that I cannot defend the conclusions of," Kirkpatrick said, according to Politico.

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An aerial photo of the Pentagon

The Pentagon is tracking some 650 instances of UFO sightings or encounters, according to officials. (STAFF/AFP via Getty Images)

A photo of a UFO image

The Pentagon has released various pieces of footage showing UFOs flying near U.S. Air Force planes. (Fox News)

Kirkpatrick was quick to clarify to lawmakers that his office has not discovered any evidence of alien activity, and such is not a focus of his office.

"I should also state clearly for the record that in our research, AARO has found no credible evidence thus far of extraterrestrial activity, off-world technology or objects that defy the known laws of physics," Kirkpatrick testified.

"Only a very small percentage of [unidentified aerial phenomena] reports display signatures that could reasonably be described as anomalous," he continued. "The majority of unidentified objects reported to AARO demonstrated mundane characteristics of balloons, clutter, natural phenomena or other readily explainable sources."

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Instead of aliens, Kirkpatrick more often considers whether an unidentified aerial phenomena (UAP) might belong to an adversary like Russia or China.

dr sean kirkpatrick

Dr. Sean Kirkpatrick, the director of the All-domain Anomaly Resolution Office, testified before the Senate Armed Services Subcommittee on Emerging Threats and Capabilities regarding UFOs, or as the military dubs them, UAPs. (U.S. Senate Committee on Armed Services)

"Of the cases that are showing some sort of advanced technical signature … I am concerned about what that nexus is," Kirkpatrick said after he was asked about Russia and China's capabilities to attack and surveil U.S. interests.

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"I have indicators that some are related to foreign capabilities. We have to investigate that with our [intelligence community] partners," he added.