In 2010, Al-Shabaab claimed responsibility for two suicide bombings carried out in Kampala, Uganda, amid crowds of soccer fans watching televised screenings of the World Cup final. The bombings left 74 people dead.
The group said at the time the attacks were retaliation for Ugandan participation in the African Union Mission in Somalia, known as AMISOM. One AMISOM goal is to support Somali government forces in cracking down on Al-Shabaab.
Al-Shabaab has also mounted many smaller attacks against targets in Kenya, hurling hand grenades into nightclubs, restaurants and schools. The group has also kidnapped tourists and aid workers.
Its attack on the Westgate mall in Kenya on September 21 killed at least 67 people.
Al-Shabaab said the attack was retaliation for Kenya's involvement in the African Union effort against the group.
In recent months, Al-Shabaab's haven in south-central Somalia has been been increasingly squeezed as Kenyan forces fight the group from the south and African Union forces come down from Mogadishu, the Somali capital.