Spanish police are looking for a vehicle rented by suspects of the Barcelona attack after reports it may have crossed into France.
A French security official said Spanish police gave them the information about the car which was rented on Thursday in Spain.
French police are on the lookout nationwide for the car which is a Kangoo utlity vehicle and were also handed information by the Spanish authorities about four suspects believed to be on the run.
France's interior minister said his country has reinforced police surveillance of what is normally an open border between the two countries.
Two men charged with murder and membership of a terror organisation as judge orders a fourth suspect to be freed on bail.
Younes Abouyaaqoub was wearing a fake bomb vest when he was killed in the town of Subirats, about 30 miles west of Barcelona.
The man believed to be responsible for driving a van into pedestrians in Barcelona has been pictured as the death toll rises to 15.