Speaking to reporters from the Somali capital, Mogadishu, al-Shabab's spokesman Ali Mohamud Rage, also known as Ali Dheere, said the twin blasts were in retaliation for Uganda's failure to withdraw its troops from Somalia.

Ugandan soldiers make up more than half the 6,100-member African Union peacekeeping force in the Horn of African country to protect the U.N.-backed Transitional Federal Government from insurgent attacks.

Ali Dheere says Uganda and the other African country contributing troops to the peacekeeping mission, Burundi, ignored previous warnings to leave Somalia.  He says the attacks were carried out to prove that al-Shabab will target civilians in Kampala and Bujumbura, if the peacekeepers are not withdrawn immediately.

Ugandan President Yoweri Museveni condemned the attacks and vowed to hunt down the perpetrators.  The country is also expected to provide the bulk of the reinforcement troops that have been pledged by East Africa's regional bloc known as IGAD to bring the peacekeeping force to its full strength of 8,000. 

Most of the casualties in the attacks were Ugandans.  But one American aid worker was killed and six Methodist missionaries from the U.S. state of Pennsylvania were wounded.