A Somalia-based terrorist group claimed responsibility for the deadly attack at a Kenyan mall on Saturday that left at least 39 shoppers dead and scores more injured.
In a series of tweets and email messages to news organizations, the hard-line Islamist group al-Shabab said it sent men armed with AK-47s and grenades into Nairobi's Westgate shopping mall as "retribution" for Kenya's efforts to help the Somalian government defeat it.
“HSM has on numerous occasions warned the #Kenyan government that failure to remove its forces from Somalia would have severe consequences,” said one tweet on al-Shabab's official Twitter account, HSM Press Office, which refers to its full name, Harakat al-Shabab al-Mujahideen
According to the U.S. National Counterterrorism Center, al-Shabab -- "the Youth" in Arabic" -- was formed in 2006 in Somalia, and soon became a major threat to the weak transitional Somali government. It was designated a terrorist organization by the U.S. in 2008 and in 2012 formally allied itself with al Qaeda.
Al-Shabab’s immediate goal is to topple the Somali Transitional Federal Government (TFG), which is supported by the African Union and Western nations, and impose Islamic Shariah law on the impoverished nation in northern Africa. But neighboring nations fear that it could have a destabilizing effect throughout the region if it were to succeed, and, led by Kenya, intervened in 2011 to halt a series of military advances by the rebels.
The U.S. has asserted that the alliance of al-Shabab and al Qaeda poses a serious threat to Western interests and has increasingly concentrated its counter-terrorism operations on al-Shabab and other groups operating in Yemen and elsewhere in North Africa.
In addition to recruiting Muslims from within Africa, al-Shabab has had success luring young Muslim men from the West to join its cause, including a number of Americans.
Among the highest-profile recruits from the West was the so-called jihadi rapper Omar Hammami, an American from Alabama reportedly killed in Somalia earlier this month after a falling out with al-Shabab's senior leader.
In May, four men in Minnesota also were imprisoned for enlisting 20 American men to travel to Somalia to fight for the terrorist group. A man from Ohio was similarly convicted in 2012 of raising money to send people from the U.S. to Somalia to aid the group in addition to sending money to Somalia for one of the recruits to buy a weapon.
Al-Shabab controlled many southern and central territories of Somalia but withdrew from Kismayo — the last of the areas it reigned — in 2012. Still, factions of the group continue to attack non-Muslims in Somalia and neighboring countries, specifically targeting governments and peacekeepers.
Most recently, al-Shabab claimed responsibility for a suicide bombing of a restaurant in Somalia that killed 15 and wounded 23 on Sept. 7.
A few days earlier, Somalia’s President Hassan Sheikh Mohamud narrowly escaped a grenade attack on his convoy that al-Shabab said it inspired.
And in late August, four Kenyan police officers were killed by 40 men, thought to belong to the terrorist group.
Reuters contributed to this report.