A massive police operation was under way in Boston early Friday after a police officer was killed on the campus of MIT and explosions and gunfire shook Watertown about 10 miles west of Boston.

In Watertown, witnesses reported hearing multiple gunshots and explosions at about 1 a.m. Friday. Dozens of police officers and FBI agents were in the neighborhood and a helicopter circled overhead.

State police spokesman David Procopio told the Associated Press, “The incident in Watertown did involve what we believe to be explosive devices possibly, potentially, being used against the police officers.”

It was unclear if the incidents were related.

FBI investigators responded to Watertown in the early morning hours, but officials declined to release details about reports of explosions and potential connections to either Monday’s Boston marathon bombings or the fatal shooting of the campus police officer.

 Officials said they are trying to piece together the chronology of chaotic early morning incidents in Watertown.

 “We are aware of the law enforcement activity in the greater Boston area. The situation is ongoing. We are working with local authorities to determine what happened,” officials said in a statement.

The MIT officer was responding to report of a disturbance Thursday night when he was shot multiple times, according to a statement from the Middlesex District Attorney’s office. The statement said the officer was transported to a nearby hospital where he was pronounced dead. It said there were no other victims.

State police spokesman Dave Procopio said the shooting took place about 10:30 p.m. outside an MIT building. The officer was described as a male, but no further information about him was released.

MIT police issued an all-clear for the campus at 1:58 a.m.

Procopio said authorities are searching for a suspect or suspects. No arrests have been made.