The suspected ringleader of the attack on the American consulate in the Libyan city of Benghazi has appeared amid tight security at a US federal court in Washington.

Ahmed Abu Khattala was captured by US forces in Benghazi on June 18. The US ambassador to Libya, Chris Stevens, and three other people were killed in the 2012 attack.

Khattala is charged with killing a person on US property, a firearms offence and providing material support to terrorism. He has repeatedly denied the charges against him.