Congressman Mark Walker, R-North Carolina, wrote a letter to Secretary of the Navy Richard Spencer requesting information about UFOs — or unidentified aerial phenomenon (UAP), as the letter says.

Walker is only the most recent lawmaker to raise concern about UAPs — Virginia Sen. Mark Warner met with Navy officials in June regarding UFO sightings by Naval aviators.

Walker expressed concern that the UAPs might be the result of advances in Chinese technology, and asked whether the sightings were being adequately researched.

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A lawmaker is raising concerns that the Pentagon isn't sufficiently investigating the strange sightings of UFOs that Navy pilots have reported.

Politico reported that Rep. Mark Walker, a Republican from North Carolina, wrote a July 16 letter to Navy Secretary Richard Spencer requesting more information about the source of the unidentified aerial phenomena, or UAP, and whether the Navy was aware of any foreign government or company that had made any significant advances in aeronautical engineering. Walker was a guest on Fox News' Tucker Carlson Tonight on July 26 to discuss his concern about the UAP that naval aviators have reported over the past four years.

"Is this something that's a defense mechanism from another country?" Walker asked during the program. "We do know that China is looking at hypersonic missiles, that's 25,000 [kilometers per hour] or to break it down into our language that's getting from D.C. where I'm at to L.A. in about nine minutes."

In the letter to Sec. Spencer, Walker stated that the unexplained encounters often "involve complex flight patterns and advanced maneuvering, which demand extreme advances in quantum mechanics, nuclear science, electromagnetics, and thermodynamics," highlighting concerns about the national security risks posed by such objects.

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The letter also expressed concern about the demise of the Advanced Aerospace Threat Identification Program (AATIP), which DoD said it shut down in 2012, according to The New York Times. "I am concerned these reports are not being fully investigated or understood," Walker's office wrote.

Walker, the ranking member of the House Intelligence and Counterterrorism subcommittee, is not the first lawmaker to express concern about unidentified flying objects.

In June, Sen. Mark Warner, a Virginia Democrat, attended a classified briefing with Navy officials regarding sightings of UFOs reported by naval aviators. At the time, a spokesperson from Warner's office told INSIDER, "If pilots at Oceana or elsewhere are reporting flight hazards that interfere with training or put them in danger, then Senator Warner wants answers. It doesn't matter if it's weather balloons, little green men, or something else entirely — we can't ask our pilots to put their lives at risk unnecessarily."

INSIDER reached out to Walker's office and to the office of the secretary of the Navy for comment, but did not receive responses by publication time.