Kenyan security forces and others gather around the scene on an attack on a bus about 50 kilometers (31 miles) outside the town of Mandera, near the Somali border in northeastern Kenya, Saturday, Nov. 22, 2014.
Kenyan security forces and others gather around the scene on an attack on a bus about 50 kilometers (31 miles) outside the town of Mandera, near the Somali border in northeastern Kenya, Saturday, Nov. 22, 2014.

Police in northeastern Kenya say al-Shabab gunmen have ambushed a bus and killed 28 non-Muslims who were singled out from the 60 passengers on the bus.

Somalia's al-Shabab Islamists have claimed responsibility for the attack, saying it was retaliation for recent raids Kenyan security forces carried out on mosques in Mombasa.

Authorities say the militants seized the bus Saturday 50 kilometers, or 31 miles, from the town of Mandera near Kenya's border with Somalia.

The White House condemned what it called a horrific attack. It said the United States stands with Kenya to counter the threat of terrorism, and it affirmed its commitment to work with Kenyans to stop such atrocities.

Kenyan troops have gone into neighboring Somalia as part of an African Union force helping Somalia put down an al-Shabab insurgency.

The al-Qaida-linked group wants to turn Somalia into a fiercely conservative Islamic state. It once controlled most of central and southern Somalia but has steadily lost ground in recent years to government and African Union forces.

Kenya has been hit by a series of gun and bomb attacks blamed on al-Shabab since Kenya sent troops into Somalia in 2011. Kenyan troops are part of the African Union Mission in Somalia that is bolstering Somalia's weak U.N.-backed government against the al-Shabab insurgency.

Al-Shabab has carried out two major attacks this year on the Somali presidential palace in Mogadishu.