Authorities in Libya have arrested four men in connection with the attack on the U.S. consulate, in which the U.S. ambassador and three embassy staff were killed, al Jazeera television reported.

The men are being questioned, Deputy Interior Minister Wanis al-Sharif said.

They are suspected of having "instigated" the attack on the U.S. compound in the eastern city of Benghazi in which U.S. ambassador to Libya Christopher Stevens died along with three other Americans.

The attack occurred during protests over a U.S.-produced film that denigrates Islam's Prophet Muhammad.

Similar demonstrations have been held across the Middle East and North Africa. In teh Egyptian capital Cairo, angry crowds have clashed with police, and Islamist groups have called for a million-strong rally later on Friday.

U.S. President Barack Obama has vowed to bring to justice those who carried out the Benghazi attack, which U.S. officials said may have been organized in advance. Secretary of State Hillary Clinton said Washington had "absolutely nothing to do" with the film, called Innocence of Muslims, which she described as "disgusting and reprehensible."

Security has been stepped up at U.S. embassies and consulates around the world following the attack, and two U.S. warships have been sent to the Libyan coast.