* Witness says non-Muslims on bus killed, Muslims spared
* Al Shabaab says attack in revenge for recent mosque raids (Adds al Shabaab statement, government official quotes)
By George Obulutsa
NAIROBI, Nov 22 (Reuters) - Somalia's al Shabaab insurgents said they staged a bus attack in northeast Kenya on Saturday that killed 28 people, all non-Muslims led out to be shot while passengers identified as Muslims were spared.
Three in the group trooped out to be killed saved their lives by reciting Koran verses for the Islamist militants, a local security official said.
Al Shabaab said its men had ambushed the Nairobi-bound bus outside Mandera town, near Kenya's border with Somalia and Ethiopia, and killed the non-Muslims in retaliation for raids on mosques in the port city of Mombasa.
Early this week, police in Mombasa shot dead a man and arrested over 376 others when they searched four mosques in the port city that they said were used to recruit militants and stash weapons.
"The Mujahideen successfully carried out an operation near Mandera early this morning, which resulted in the perishing of 28 crusaders, as a revenge for the crimes committed by the Kenyan crusaders against our Muslim brethren in Mombasa," Sheikh Ali Mohamud Rage, al Shabaab's spokesman, said in a statement.
Islamist militants use the term "crusaders" to describe Christians or non-Muslims in general.
Police Inspector General David Kimaiyo told reporters that 19 men and nine women were killed. "Preliminary reports indicate that the attackers, who were heavily armed, later fled towards the border into Somali," he said.
A witness to the ambush, who asked not to be identified, said the attackers entered the bus and greeted passengers before trying to identify Muslims and non-Muslims.
Ahmed Maalim, an official at the Mandera East sub-county security force, said the attackers ordered passengers thought to be non-Muslims out of the bus. Three were spared after reciting Koran verses and ordered back into the bus.
"The women and men (remaining outside) were separated, then shot at close range. None survived," he said Maalim.
Al Shabaab, which was behind a bloody 2013 attack on Nairobi's Westgate shopping mall, has vowed to drive Kenyan and other African Union peacekeeping troops out of Somalia.
The Mandera region is also awash with guns due to its proximity to Somalia, where al Shabaab has been fighting to topple the government, and Ethiopia, whose armed Oromo Liberation Front has made incursions into Kenya.
Insecurity plagues East Africa's biggest economy, prompting Western nations to issue travel warnings and hitting the tourism industry, a major source of hard currency. (Additional reporting by Feisal Omar and Abdi Sheikh in Mogadishu, Humphrey Malalo in Nairobi, Noor Ali in Isiolo; Editing by Tom Heneghan)
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