A letter bomb sent to an American physical therapist exploded as the man was opening it Wednesday, inflicting multiple wounds, a senior police official said.

The unidentified man was injured in his face, hands and left leg, said the police chief of the eastern city of Khobar, Naser Mohammed al-Naser.

He said the man, who was taken to a local hospital, worked as a physical therapist and had presumed the parcel contained a video tape.

Al-Naser gave no details about his identity or the extent of his injuries.

A U.S. Embassy official in the Saudi capital, Riyadh, confirmed an American man was "wounded" in an explosion in Khobar. He gave no other details and spoke on condition of anonymity.

There have been a string of suspicious bombings in Saudi Arabia since November, one of them in Khobar, where a 1996 bomb attack against a U.S. military barracks killed 19 American airmen. A Scottish man was injured in a small explosion in Khobar last December.

A British man and an Egyptian were injured in a bomb blast in Riyadh in March, and two other bombs in the capital between Nov. 17 and Dec. 15 killed a Briton and injured four others.

Three foreigners working in Saudi Arabia -- a Briton, a Belgian and a Canadian -- have been arrested in connection with the bombings and remain in custody. The three appeared on Saudi state television in February and confessed to carrying out the bombings, according to the station's Arabic translations of their statements.

The Saudi Interior Minister, Prince Nayef, has said that authorities knew who was behind the attacks, but he did not give any other information. He said the explosives used in the bombings were made by experts.

Neither the suspects who spoke on television nor Saudi officials have given the motive for the bombings. Nayef has said authorities do not suspect a political motive.