Libyan interim president Mohammed Magarief has suggested al-Qaeda played a part in the attack on the US consulate in Benghazi in which four Americans, including the ambassador, to Libya died.
The attack on Tuesday came amid protests over a video made in the United States that Muslims saw as blaspheming the Prophet Mohammad.
It resulted in the deaths of the US ambassador Christopher Stevens and three other Americans.
Mr Magarief told CBS about 50 people had been arrested in connection with attack. Some of those arrested were not Libyans and were linked to al-Qaeda, he said.
He described others as affiliates or sympathisers. "It was definitely planned by foreigners, by people who entered the country a few months ago," he said, adding that some were from Mali and Algeria.
The United States wants the FBI to investigate the consulate attack, but the Libyan leader said it may be too soon to send in investigators.
Mr Magarief says there is little doubt the assault was planned rather than a spontaneous reaction to the video, citing the fact that it came on the 11th anniversary of the 9/11 attacks.
The US ambassador to the United Nations, Susan Rice, said on talks shows on Sunday preliminary information indicated the consulate attack was not planned.