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.
Four of the five suspected terrorists in the Cambrils attack were shot dead by the same police officer.
The group were all killed after ramming their car into a group of people in the Spanish coastal town on Friday morning.
Several pedestrians were injured, one who later died in hospital, just hours after a similar incident in Barcelona where 13 people were left dead.
Catalonian authorities tweeted that the same police officer had shot dead four of the five Cambrils attackers.
Footage of the assailants lying dead on the ground showed they had been wearing fake suicide belts.
The Queen has sent her condolences to the King of Spain in the wake of the country's two terror attacks.
Her Majesty described events in Barcelona and Cambrils, where 14 people were killed, as "deeply upsetting".
In her message to King Felipe, the Queen said: "It is deeply upsetting when innocent people are put at risk in this way when going about their daily lives.
"Our thoughts and prayers are with those who have lost loved ones and the people who are recovering in hospital."
The Spanish royal, who made a state visit to the UK last month, joined thousands of people in Barcelona for a minute's silence on Friday.