Three teenagers were killed and another youth was critically injured Saturday in a garage explosion at the home of a Brazilian embassy employee, police said.

Montgomery County Police Sgt. Harry Geehreng said the explosion apparently was caused by some type of bomb, but he said investigators have concluded that the blast was not caused by terrorists.The incident occurred before dawn Saturday as the four youths were attempting to make a bomb while their parents were asleep, according to local police officials.

After a preliminary investigation by Montgomery County Police, spokeswoman Ann Evans said that "there is a strong suggestion that the four boys were experimenting with some type of explosives."

Two of the victims were killed instantly by the blast, while the third person died a short time after being rushed to a local hospital, Geehreng said.

He said the explosion damaged a car in the garage, but there was no evidence that a bomb had been placed in or under the vehicle.

"We don't know the cause of the explosion yet," said Geehreng. "We'll probably be here all day sifting through debris."

Geehreng said he could not release the identities of those killed or injured.

The explosion occurred at about 3:10 a.m. at the Bethesda home of Vera Machado, said Geehreng. Machado and her husband, Richard, were sleeping inside the home and were not injured, he said.

A security guard who answered the telephone at the Brazilian embassy in Washington said Machado was a consular attache. The guard, who refused to give his name, said he did not know her duties.