In an audio message posted on Somalimemo.net, Mukhtar Abu Zubeyr, known as Godane, said Saturday's attack on the upscale Westgate mall was an act of revenge by Al Shabaab for the Kenyan army's incursion into southern Somalia to eliminate Islamist extremists.
At least 72 people - including 61 civilians - were killed in the attack, which began Saturday and ended Tuesday after a four-day standoff.
"Remove your troops or prepare for a long, bloody war. Decide now and withdraw your troops from the Islamic regions of Somalia," Al Shabaab's leader said.
"If not, be ready for more bloodshed in your territory, for economic collapse, and to see yourselves displaced," Godane said.
Islamist radicals have threatened to carry out reprisal attacks on Kenya since October 2011, when the Kenyan army invaded Somalia to assist African Union peacekeepers and the Somali government in their fight against Shabab.
That military intervention followed a spate of kidnappings allegedly carried out by Al Shabaab on Kenyan soil.
At least two policemen were killed Thursday and two others were wounded in an armed attack in the northeastern Kenyan town of Mandera, which borders Somalia and Ethiopia.
That attack came a day after a similar incident Wednesday in the eastern Kenyan town of Wajir - 100 km from the Somali border - left one dead.
Both Wajir and Mandera have been the target of various attacks that the Kenyan authorities blame on Al Shabaab.
That group, which formally declared allegiance to Al Qaeda in 2012, has been battling Somalia's government since 2006 in a bid to establish a fundamentalist Islamic state in that East African nation.
Islamist militants control much of central and southern Somalia, which has been beset by civil war since military dictator Siad Barre was overthrown in 1991.
--IANS (Posted on 26-09-2013)