Authorities have opened a terrorism investigation after an explosion outside a synagogue in southwestern France injured a police officer. Two cars parked at the Beth Yaacov synagogue complex in the seaside resort town of La Grande Motte near Montpellier were set on fire just after 8am local time, the National Antiterrorism Prosecutor’s Office said in a statement. Firefighters discovered additional fires at two entrances to the synagogue. A police officer who walked up to the site was injured after a propane gas tank in one of the vehicles exploded, the statement said. Five people, including th…