In a ruling issued Tuesday, Supreme Court Justice John Paul Stevens said Samantar was not protected by diplomatic immunity, and can be sued.
Samantar, who now lives in the U.S. (in the state of Virginia), served as Somalia's defense minister in the 1980s and then as prime minister from 1987 to 1990.
Members of Somalia's Isaaq clan filed the original lawsuit under a 1991 U.S. law called the Torture Victim Protection Act. The lawsuit accuses the former prime minister of commanding the country's military force to torture, kill, and arbitrarily detain clan members and their families.
A federal judge had originally ruled that Samantar was entitled to diplomatic immunity. An appeals court reversed that decision and the Supreme Court Tuesday upheld it.