LONDON - Britain's Foreign Office issued an alert warning British citizens in the Nice area in France to follow the instructions of the French authorities after a Bastille Day attack killed 73 in the Riviera city. An attacker drove a truck at high speed into a crowd watching fireworks late on Thursday, local media quoted officials as saying. 'We are in touch with the local authorities and seeking more information following an apparent attack on a Bastille Day celebration in Nice. If you are in the area follow the instructions of the French authorities,' the Foreign Office said in updated travel advice on France.