MEXICO CITY (Reuters) - The Mexican Air Force has released footage of what a UFO expert says are 11 invisible unidentified flying objects picked up by an infrared camera as they whizzed around a surveillance plane.

A long-time believer in flying saucers, journalist Jaime Maussan told a news conference on Tuesday the objects were real and seemed "intelligent" after they at one point changed direction and surrounded the plane chasing them.

"They were invisible to the eye but they were there, there is no doubt about it. They had mass, they had energy and they were moving about," he said, after showing a 15-minute video he said the Defense Ministry gave him permission to publicise.

The ministry confirmed to Reuters it had provided the video, filmed by the Air Force on March 5 over the eastern coastal state of Campeche.

"We are not alone! This is so weird," one of the pilots can be heard yelling, after the plane's crew switched on an infrared camera to track the objects, first picked up by radar.

The film, recorded by a plane looking for drugs trafficking near the Gulf of Mexico, shows 11 objects as blobs of light that hover in formation or dart about, sometimes disappearing into cloud.

Mexico's most popular nightly news broadcast showed the video on Monday night.

Interviewed by Mausson on another section of the video, the pilots said they grew nervous when the objects, still invisible, turned back during a chase and surrounded the plane.

"There was a moment when ... the screens showed they were behind us, to the left and in front of us. It was at that point that I felt a bit tense," said Major Magdaleno Castanon.

Mexico has a long history of fanciful UFO sightings, most of which are dismissed by scientists as space debris, missiles, weather balloons, natural weather phenomena or hoaxes.