A Boston police officer found a burning propane tank near an unoccupied police cruiser on Friday but drove the car away before the tank detonated and no one was hurt in the blast, a police spokeswoman said.
Police and federal law enforcement officials are interviewing witnesses and reviewing surveillance video to try to determine who left the tank next to the parked vehicle near a police station in the south of the city, said Boston Police Department spokeswoman Rachel McGuire.
The Boston Globe quoted the police commissioner, William Evans, as saying it was a "deliberate act" aimed at blowing up the cruiser, and saying the federal Joint Terrorism Task Force was called in to help with the investigation.
Police were on high alert nationwide on Friday as Donald Trump was due to be sworn in as the 45th president of the United States. Activists have scheduled anti-Trump protests around the country, including in New York, Chicago and Boston.