CAMP FOSTER, Okinawa — No Marines were injured Wednesday when their 7-ton truck broke down and caught fire on the Okinawa Expressway, a Japanese police spokesman said.

Two members of 3rd Marine Logistics Group were northbound in the truck — officially called a medium tactical vehicle replacement — around 8:40 a.m. in Kitanakagusuku village when they experienced engine trouble and pulled to the roadside, a spokesman for Okinawa Prefectural Police said by phone Friday.

An expressway administrator then called police to report smoke emanating from the engine compartment.

The fire quickly spread and soon engulfed the cab, the spokesman said. Firefighters extinguished the blaze in about 30 minutes. Expressway traffic backed up over two miles during the incident, he said.

The cause of the fire is under investigation, logistics group spokesman 1st Lt. Samuel Barge wrote in an emailed statement Friday.

Some government officials in Japan may speak to the media only on condition of anonymity.