Al-Shabab is an extremist Somali organization, formed from the remnants of an Islamic government overthrown in 2006, that sees African Union peacekeepers as invaders. It has its headquarters in Mogadishu. Self-described as "Somalia’s Islamic movement", the group has "threatened to take control of Somalia and had confined the interim government to one farming town until neighboring Ethiopia intervened." The aim of al-Shabab is the institution of Sharia law.
The organization had a rapid expansion and is considered to have ties to Al Qaeda. Some Americans and Europeans are also present in its camps.
"There is increasing concern about what terrorists operating in Somalia might do," a U.S. counterterrorism official said. According to other senior officials, the camps have graduated hundreds of fighters. 
- United States Designates Somalia's al-Shabab as a Terrorist Group
- Capture Pirates, on Land and Sea The New York Times.