Cambodian Prime Minister Hun Sen on Thursday expressed his sympathy to the United States and the victims of Boston Marathon bombings, which killed three people and injured 170 others.

"I'd like to extend my sympathy to the United States and the victims' families in the blasts," the premier said during the inauguration of Kampot province's new administration building.

Twin explosions occurred near the finish line of the Boston Marathon on Monday, Among those killed were an eight-year-old boy and a female Chinese student.

The U.S. authorities have called the bombings an "act of terror ", but the motives and perpetrators remain unknown.