French police searched the hotel rooms and team bus of the Bahrain Victorious cycling team taking part at the Tour de France in an anti-doping raid that went on for several hours overnight.

The raid took place late Wednesday and carried on until around 2a.m., sources close to the investigation told AFP in Pau on Thursday.

Bahrain Victorious has won two stages on the 2021 edition: Slovenian rider Matej Mohoric claimed stage seven and Dylan Teuns triumphed on stage eight.

The team's climb specialist, Wout Poels of the Netherlands, wore a grim smile as he lined up on the front row of stage 18 on Thursday wearing the polka dot king-of-the-mountains jersey.

The team's press officer said his team had complied with all that was requested of them, and that they were now expecting an explanation for the raid.

The Movistar team were at the same hotel as Bahrain Victorious but no searches were carried out on the Spanish team in the overnight operation in the Basque town of Pau.

The police unit concerned confirmed the raids and said files on the riders had been confiscated.

The sports director of the team, Croatian Vladimir Miholjevic, said his riders were shaken.

"Following stage 17, we were greeted by several French police officers. We were not given a warrant to read through, but the team complied with all the officers' requests," he said.

"The process had impacted our riders' recovery and meal planning," he said after access to team facilities was temporarily denied overnight.

The outfit, which leads the Teams standings and has riders in contention for the points and climbing jerseys, said they had fully cooperated with the police.

"We are committed to the highest level of professionalism and adherence to all regulatory requirements," said Miholjevic.

Police told AFP the affair was in its preliminary stages.

"A preliminary enquiry has been opened to see if there has been, or not, acquisition, transport or possession of banned substances," the Marseille-based police unit dealing with public health matters overseeing the matter told AFP.

The team have had excellent results on recent races such as the Giro d'Italia and the Tour de France warm-up, the Criterium du Dauphine.

After Thursday's stage leader of the rival UAE Emirates team Tadej Pogcar, the overall leader of the 2021 Tour de France described the raid as strange.

"Its something strange, maybe it's just one more control to see nobody's hiding anything," said Pogacar.

"We just found out in the morning, it's strange, I don't know what to think," he said.

The president of the anti-doping group Movement for Credible Cycling (MPCC) told AFP much needed to be done in the fight to find cheats.

"We can see doping controls are taking place but the doubts linger, we have to try and diminish those doubts," Roger Legeay said.

The Bahrain team was created in 2017 and qualified for the elite-level World Tour in its first season.

Team general manager Milan Erzen of Slovenia, whose name was cited in the "Aderlass" investigation into an international blood-doping ring, has vigorously denied previous anonymous accusations of doping by the Bahrain outfit.

The Tour winds up on the Champs-Elysees on Sunday.