WASHINGTON (AFP) - The suspected ringleader of a deadly 2012 attack on the American consulate in the Libyan city of Benghazi arrived in the United States on Saturday in the custody of US authorities, a justice official said.

"Ahmed Abu Khatallah is in law enforcement custody," a Department of Justice spokesman said in an email to AFP, declining to give further details.

Four Americans including US ambassador Christopher Stevens were killed on September 11, 2012 in Benghazi when gunmen stormed the US consulate and set it on fire, and a CIA outpost was also targeted.

US commandos captured Khatallah earlier this month in a covert raid on Libyan soil and he was transferred to the United States after being interred on a US vessel.

Special forces, working with FBI agents, carried out the stealth operation to seize Khatallah - whom the US has accused of being the attack ringleader - under cover of darkness and withdrew without losses. Libya accused Washington of violating its sovereignty.

The raid represented a victory for President Barack Obama, who has faced intense criticism over his administration's handling of the Benghazi assault and its aftermath.