Eurostar trains to London and all trains heading to northern France were brought to a halt on Friday following the discovery of an unexploded bomb dating back to World War II near the tracks in the Seine-Saint-Denis region. 

France’s national train operator SNCF said in a statement that traffic would be stopped at the Gare du Nord—a major European transit hub—until mid-morning at the request of police. “We invite travellers to postpone their trip,” it said.