The United States is deploying a US Marine anti-terrorism team to Libya to bolster security after a deadly attack on the American consulate in Benghazi, a US defense official said Wednesday.

"The Marines are sending a FAST (Fleet Antiterrorism Security Team) team to Libya," the official, who spoke on condition of anonymity, told AFP.

The decision to move the roughly 50-member unit to Libya comes after Washington's ambassador to Tripoli and three other Americans were killed when a mob stormed the US consulate in Benghazi.

The crowd had been angered over an amateur American-made film mocking Islam, after video clips from the movie had been posted on the Internet.

The low-budget movie, "Innocence of Muslims," in which actors have strong American accents, portrays Muslims as immoral and gratuitously violent.

President Barack Obama quickly ordered increased security at US diplomatic posts around the world, while denouncing Tuesday's deadly assault in Benghazi – an Islamist stronghold in eastern Libya – which coincided with the anniversary of the September 11 attacks in the United States.

US Marines and private contractors are charged with safeguarding diplomatic posts abroad and it was unclear how the attackers managed to breach security.

The Fleet Anti-terrorism Security Teams, under the authority of the US Navy's chief of operations, were formed in 1987 to provide a fast response to security threats after a series of terror attacks in the 1980s and 1970s.

"These companies are called on to protect forces and installations when a heightened security threat requires it," states the unit's website.