France became the first country to open its files on UFOs Thursday when the national space agency unveiled a website documenting more than 1,600 sightings spanning five decades.

The online archives, which will be updated as new cases are reported, catalogues in minute detail cases ranging from the easily dismissed to a handful that continue to perplex even hard-nosed scientists.

"It is a world first," said Jacques Patenet, the aeronautical engineer who heads the office for the study of "non-identified aerospatial phenomena."

Known as OVNIs in French, UFOs have always generated intense interest along with countless conspiracy theories about secretive government cover-ups of findings deemed too sensitive or alarming for public consumption.

"Cases such as the lady who reported seeing an object that looked like a flying roll of toilet paper" are clearly not worth investigating, said Patenet.

But many others involving multiple sightings -- in at least one case involving thousands of people across France -- and evidence such as burn marks and radar trackings showing flight patterns or accelerations that defy the laws of physics are taken very seriously.

A phalanx of beefy security guards formed a barrier in front of the space agency (CNES) headquarters where the announcement was made, "to screen out uninvited UFOlogists," an official explained.

Of the 1,600 cases registered since 1954, nearly 25 percent are classified as "type D", meaning that "despite good or very good data and credible witnesses, we are confronted with something we can't explain," Patenet said.