The group said the attack is "retributive justice for crimes" committed by Kenya's military, and "now it's time to shift the battleground and take the war to their land."
The group said the message sent to the Kenyan government and public "is and has always been just one: remove all your forces from our country."
The East African country has been scrambling with insecurity since October 2011, when the Kenya Defense Forces launched a cross- border incursion into southern Somalia in pursuit of Al-Shabaab militants, who had kidnapped several foreigners on the side of Kenya along the border, posing a serious threat to the country's pillar industry of tourism.
In the latest development, Kenyan police said they are holding a suspect in connection to the attack. Inspector General of Police David Kimaiyo said the suspect believed to have been involved in the attack was escorted to hospital by police in an operation carried out by a contingent of police officers who have surrounded the mall.
"We have detained the Westgate Mall attack suspect in hospital. One gunman was wounded while several others have been pinned down, " Kimaiyo told a news conference in Nairobi.
Kenyan presidency later confirmed that the gunman who had been arrested succumbed to bullet wounds.SHOOTING SPREE
The standoff continues into the evening, hours after the shootout between police officers and the armed men in the mall began in the morning.
Authorities have already moved in elite troops with the backing of armored vehicles to reinforce the police force surrounding the shopping mall, which is frequented by wealthy Kenyans and foreigners. The mall consists of five floors and more than 80 shops as well as a Nakumatt supermarket which is occupied by masked gunmen, according to police.
Witnesses said they thought it was a robbery after they heard of explosion and gunshots. Mutea Iringo, the principal secretary in the ministry, said it was an terror attack rather than a robbery. After the attack, the Google Kenya has also been hacked.
A witness who did not give the name told Xinhua that he heard explosion and saw masked gunmen shooting before he hid in a men's room. He said the gunmen were speaking the language that he did not understand.
Another anonymous witness said the gunmen shot dead the security guards and then opened fire shop by shop.
The group of gunmen entered the mall at around 10:30 a.m. local time. However, they did not say anything conclusive about their demands.
A hostage freshly released by the captors reported machine-gun shooting at crowds of shoppers and many bodies on the ground after the killing spree.
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