CHICAGO — Five drunken French tourists landed in a Texas jail Wednesday after breaking into a county courthouse in the middle of the night and sparking terrorism fears, officials said.

Security footage showed the men wearing sombreros and playing around with a judge's gavel before they were arrested by police, who were tipped off by the courthouse security system at around 1:30 am (0630 GMT).

But since they'd left the sombreros behind as they made their way out of the building, the responding officers were worried at first that it could be some kind of terror plot.

They called for a security sweep of the building and shut down neighboring streets in downtown San Antonio for several hours.

Soon the local media was "breathlessly" reporting that the courthouse had been attacked, Bexar County spokeswoman Laura Jesse told AFP.

Reports surfaced that two of the men were on an FBI watch list and that photos of critical infrastructure -- water systems and courthouses -- were found in their recreational vehicle.

But after the security tapes were reviewed and the men questioned, it became pretty clear that the break-in was simply a stupid "prank," she said.

"It's pretty entertaining at least," Jesse said.

"Usually when you think of someone trying to commit a terrorist attack it's not with a sombrero and waving a gavel."

An FBI spokesman declined to comment on whether any of the three brothers or their two friends were on a terrorism watch list but noted "we have found no public safety threat."

"We still have an ongoing inquiry, we're still searching a few aspects about these individuals," special agent Erik Vasys of the San Antonio office of the FBI told AFP.

"We're not classifying or qualifying whether it's a prank or not at the moment."

Local officials were puzzled by the motive, but not the severity of the crime.

"At this point we do not believe nor do we have any evidence of a terrorist plot," said sheriff's department spokesman Ronald Bennett.

"We believe at this point the five individuals were here to see our country and after a night of drinking on the famous San Antonio River walk, things spun out of control and they decided to unlawfully enter a building. The reason why they entered the historic courthouse is unknown."

Only two of the men were arrested in the building. Three others were found in the RV which was parked outside.

The five men aged 21 to 27 are currently being held on burglary charges.

An official told AFP on condition of anonymity earlier Wednesday that the men were believed to be of Moroccan descent and that it was not yet clear whether they held French, Moroccan or dual nationalities.

They were later confirmed to be French nationals, according to another official who declined to be named.

Officials also bumped up security at a conference being held nearby about satellites and other national security tools used to monitor possible terrorist activities.

"It's a serendipitous event, as far as I know right now," conference organizer Keith Masback, with the United States Geospatial Intelligence Foundation, told KSAT news.

"But it just heightens our awareness and heightens our resolve that what we're doing here this week is critically important for the nation."