The U.S. government has often ignored the possibility of unidentified flying objects, even after decades of unexplained sightings, including by U.S. military pilots who sometimes filmed the UFOs, some of which moved with lightning speed and incredible agility.

On Tuesday, a congressional hearing focused on UFOs for the first time in 50 years, this time looking at their threat to national security - not from people from other worlds, but from potential international adversaries on Earth.

The hearing came nearly a year after a government report documented more than 140 cases of unidentified aerial phenomena, or UAP, that U.S. military pilots had observed since 2004.

'They are real. They need to be investigated. And any threats they pose need to be mitigated,' said Representative Andre Carson, chair of the House Intelligence Subcommittee on Counterterrorism, Counterintelligence and Counterproliferation.

During his testimony, Undersecretary of Defense for Intelligence and Security Ronald Moultrie said, 'We're open to all hypotheses. We're open to any conclusions that we may encounter.'

'The stigma associated with UAPs has gotten in the way of good intelligence analysis. Pilots avoided reporting or were laughed at when they did,' Carson said. 'Today we know better.'

Moultrie, who oversees the Pentagon-based UAP investigation team, added that 'because UAP pose potential flight safety and general security risks, we are committed to a focused effort to determine their origins.'

The hearing focused on possible foreign adversaries of the U.S. developing secret technologies that could be construed as UFOs and prove detrimental to the United States.

'The intelligence community has a serious duty to our taxpayers to prevent potential adversaries, such as China and Russia, from surprising us with unforeseen new technologies,' said Republican Representative Rick Crawford.

While testifying, Deputy Director of Naval Intelligence Scott Bray showed UAP video clips. One showed flashing triangular objects in the sky, later determined to be visual artifacts of light passing through night-vision goggles. In another, a shiny spherical object zipped past a military aircraft's cockpit window - an observation Bray said remained unexplained.

Although Bray did not rule out extraterrestrial origins, he said there hasn't been anything to suggest the sightings are 'nonterrestrial in origin.'

The number of UAPs in the military database has grown to about 400, Bray said.

They are increasing, he noted, likely because of technological advances, such as better sensors, and expanded drone usage.

Bray cautioned the committee about the need to balance transparency with the protection of sensitive intelligence information.

'Given the nature of our business, national defense, we've had to sometimes be less forthcoming with information in open forums than many would hope,' he said. 'We do not want potential adversaries to know exactly what we're able to see or understand or how we come to the conclusions we make,' he said.