The U.N. Security Council on Wednesday blacklisted two branches of the Islamist extremist group Ansar al-Sharia in Libya, which Washington says was behind the 2012 Benghazi attack that killed the U.S. ambassador and three other Americans.

Ansar Al Sharia Benghazi and Ansar Al Sharia Derna, both associated with al Qaeda, were added to the al Qaeda sanctions list and will face an arms embargo and a global travel ban and asset freeze, U.N. diplomats said.

"Both groups are responsible for acts of terror in Libya, including bomb attacks, kidnappings, and murder," British Foreign Secretary Philip Hammond said in a statement. Britain, France and the United States initiated the action.

Ansar Al-Sharia is one of a slew of violent political factions and tribal groups fighting for power since the government lost control of the capital, Tripoli.

The U.N. Security Council has had an arms embargo and other sanctions on Libya since 2011, when former leader Muammar Gaddafi cracked down on pro-democracy activists. Gaddafi was ousted from power and killed later that year.

Separate from the U.N. sanctions, the United States is also considering imposing sanctions on Libya's militants to try to force leaders to negotiate and prevent the country from descending further into chaos.