The Pentagon is creating a new office to investigate unidentified flying objects amid concerns that after broad probes it cannot explain mysterious sightings near highly sensitive military areas.

Deputy Secretary of Defense Kathleen Hicks, working with the US director of national intelligence, ordered the new investigatory body to be established in the US Defense Department's intelligence and security office, the Pentagon said late Tuesday.

The order came five months after a classified US intelligence report on possible alien UFOs came up inconclusive: it could explain some reported incidents but was unable to account for other phenomena, some filmed by pilots near military testing areas.

The new office will focus on incidents in, or near, designated "special use airspace" (SUA) areas strictly controlled and blocked from general aviation due to security sensitivities.

The US military is worried some of the unidentified aerial phenomena spotted by military pilots in the past may represent technologies of strategic rivals unknown to US scientists.

"Incursions by any airborne object into our SUA pose safety of flight and operations security concerns, and may pose national security challenges," the Pentagon said in a statement.

The Defense Department "takes reports of incursions -- by any airborne object, identified or unidentified -- very seriously, and investigates each one," it added.

The new office was dubbed the Airborne Object Identification and Management Synchronization Group (AOIMSG), the successor to the US Navy's Unidentified Aerial Phenomena Task Force.

It will be overseen by a panel of experts from the military and intelligence community.

A mostly classified official review of UFO reports released in June determined that most of around 120 incidents over the past 20 years could be explained and had nothing to do with unknown or secret US or foreign technology.

But it could not explain some beguiling reports and videos made by military personnel.

Last year, the Pentagon released a still inexplicable video taken by navy pilots of objects moving at incredible speeds, spinning and mysteriously disappearing.

China's July test of a globe-circling hypersonic vehicle that was able to launch a separate missile while traveling at more than five times the speed of sound alerted Washington that Beijing might have technologies the United States has yet to develop.