A top Republican on the House Homeland Security Committee is accusing the Navy of withholding information about reports of unidentified aircraft after officially requesting more data on the mysterious encounters.

Rep. Mark Walker of North Carolina, the ranking member of the Intelligence and Counterrorism subcommittee, asked Secretary Richard V. Spencer in July to outline what resources the Navy is dedicating to investigating the sightings. He also asked if officials have found "physical evidence" to substantiate the claims, and whether they are aware of any foreign nations or private companies that have introduced breakthrough technologies that could explain them.

Navy Undersecretary Thomas Modly responded in a brief letter on July 31 that "the Department of the Navy takes these reports very seriously and continues to log sightings and fully investigate the accounts," according to a copy provided to POLITICO.

But Walker said he is discouraged by the Navy's seeming unwillingness to provide his committee with more data about the so-called unidentified aerial phenomena — the term the Pentagon prefers over the more traditional "unidentified flying objects," or UFOs. He has expressed concern publicly that the craft could pose a threat to U.S. forces or territory.

“While I am encouraged the Under Secretary of the Navy confirmed that UAP encounters are fully investigated, there is frustration with the lack of answers to specific questions about the threat that superior aircraft flying in United States airspace may pose," Walker told POLITICO in a statement.

Navy spokesperson Joe Gradisher responded that the service is prepared to accommodate any further congressional requests for information. "At this point in time, however, we have not received any new requests for updates on this issue," he said by email.