An unexplained “flash fire” atop a District streetcar late Saturday is under investigation, city officials said Sunday.

In a statement, the District’s Department of Transportation said “initial observations suggest this was an isolated incident,” but transportation officials did not explain why they think that to be the case or provide details on a possible cause.

D.C. police Officer Frederick Lee said there were a pair of streetcar incidents Saturday night. They coincided with the icy storm that was making its way over the city and the 2.2 mile H Street/Benning Road NE streetcar line. Safety concerns have repeatedly delayed the opening of the line to passengers, and on Saturday the line was undergoing its latest round of “simulated service,” transportation officials said.

In one incident Saturday, there was a report about 10 p.m. that “a streetcar sideswiped and damaged a vehicle” in the 500 block of H Street, police spokeswoman Aquita Brown said. Another incident took place near the 1200 block of H Street, Lee said.

At about 11:45 p.m., “a brief flash fire was ignited on top of the streetcar vehicle,” DDOT said.

“The sparks extinguished very quickly on their own and fire suppression was not required by the first responders on the scene. The vehicle operator was safe due to the vehicle’s insulation from electrical current,” DDOT said.

The streetcar’s “fail-safe” mode kicked in and the vehicle stopped, DDOT said. Power to the overhead lines was shut off, and the streetcar was dragged to a maintenance yard on Benning Road. Another streetcar “was immediately put into operations and ran without incident,” DDOT said.

There have been multiple streetcar incidents in recent months, raising questions about the alignment of tracks along H Street and Benning Road and the system’s overall design. The tracks are close to cars parked along H Street curbs. On Benning, the tracks generally run next to the median and federal safety officials have raised concerns about pedestrian safety there and elsewhere on the line.

DDOT spokesman Reggie Sanders did not immediately answer questions Sunday about the amount of damage the fire caused to the streetcar in the latest incident and what needs to be done to get the car back in service. Sanders also would not address police information describing two incidents. DDOT’s statement refers to a single incident. Fire officials did not respond to queries.

The streetcar’s manufacturer will take part in the investigation, and streetcar officials are “embarking upon a full inspection of the entire system,” DDOT said. A “top to bottom review” of the system is ongoing, DDOT noted.

Mayor Muriel E. Bowser’s new DDOT chief, Leif Dormsjo, said after his appointment in January that he would have the American Public Transportation Association bring in a team of industry experts to examine the city’s streetcar system. He said last week that the team is expected to take weeks to do its work and provide a list of steps the city can take to improve the streetcar line before people start riding. Dormsjo said he is working with the Federal Transit Administration and the city’s state safety oversight office to address concerns.