Islamist terror group al Shabab claimed responsibility for a horrific 26/11 style terror attack on an upscale Nairobi mall on Saturday afternoon. Here are some key facts about the group.

Islamist terror group al Shabab claimed responsibility for a horrific 26/11 style terror attack on an upscale Nairobi mall on Saturday afternoon local time, saying that it was in retaliation for Kenya's military involvement in Somalia.

The attack has killed at least 43 people and injured more than 200, according to the latest reports. However this toll is likely to rise further, especially since a number of gunmen are still holed up inside the mall with an unspecified number of hostages.

Shortly after the attack, al Shabab claimed responsibility via its Twitter feed, and said that it has many times warned Kenya’s government that failure to remove its forces from Somalia “would have severe consequences.”

“The attack at #WestgateMall is just a very tiny fraction of what Muslims in Somalia experience at the hands of Kenyan invaders,” al-Shabab said.

Another tweet said: “For long we have waged war against the Kenyans in our land, now it’s time to shift the battleground and take the war to their land #Westgate.” Al-Shabab’s Twitter account was suspended shortly after its claim of responsibility and threats against Kenya. Twitter’s terms of service forbids making threats.

Here are some key facts about the group:

* al-Shabaab is a Somali offshoot of the al-Qaeda. However as this CNN analysis report notes, Al-Shabaab has long been regarded as a regional offshoot of al-Qaeda, its leaders only declared their formal ties to the international terror organization in February 2012. al-Shabaab means 'The youth" in Arabic.

* The group is fighting to establish a strict Islamic state in Somalia. The group describes itself as waging jihad against "enemies of Islam"

* Its indiscriminate bombing strategies that saw many civilian and Muslim casualties came in for criticism from other branches of the al Qaeda including Osama Bin Laden himself. It is noteworthy that the group reportedly escorted Muslims out of the mall before indiscriminately firing and throwing grenades inside.

* al-Shabaab was originally engaged in combat with the Somali government and a multinational force called AMISOM, the African Union Mission in Somalia, which has been conducting peacekeeping operations with the backing of the United Nations.

Led by Uganda’s army, AMISOM succeeded in forcing al-Shabab to retreat from Mogadishu, Somali’s capital, in 2011. Last year, more than 2,000 Kenyan troops joined hands with a Somali clan to evict al-Shabab from its last urban stronghold, the port town of Kisimayo.

However it evolved its fighting methods - Instead of force-on-force fighting with AMISOM, it switched to terrorism.“By avoiding direct military confrontation”, according to a UN report, “it has preserved the core of its fighting force and resources”.

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* The once ragtag affiliate has grown into an economic powerhouse, raising tens of millions of dollars in cash from schemes that have involved extortion, illegal taxation and other "fees," according to a 2011 United Nations report.

* According to the US National Counter terrorism centre, "al-Shabaab is not centralized or monolithic in its agenda or goals. Its rank-and-file members come from disparate clans, and the group is susceptible to clan politics, internal divisions, and shifting alliances."

* According to this CNN report, "The group is believed to be responsible for attacks in Somalia that have killed international aid workers, journalists, civilian leaders and African Union peacekeepers. It has struck abroad, too. It was responsible for the July 2010 suicide bombings in Kampala, Uganda, that killed more than 70 people, including a U.S. citizen, as they gathered to watch a World Cup final soccer match.

With inputs from agencies