UPDATE: How al-Shabab militants killed passengers who couldn’t read Quran

Details have emerged as to how scores of Islamic militants, al-Shabab, attacked a bus and killed 28 passengers on Saturday morning, in the Kenyan town of Mandera which borders Somalia. The bus was said to be heading to Nairobi, Kenya’s capital.

One of the passengers on the bus, Ahmed Mahat, told the BBC that the bus was stopped and the 60 passengers ordered off board and grouped into two - Somalis and non-Somalis.

According to Mahat, "The non-Somalis were ordered to read some verses of the holy Koran, and those who failed to read were ordered to lie down. One by one they were shot in the head at point blank range."

Kenya’s interior ministry said security agencies were “in pursuit of the criminal gang”.

The attack comes a week after security forces raided mosques in Mombasa saying they were being used to store weapons. The raids triggered reprisal attacks by Muslim youths.

Kenya has experienced a series of al-Shabab attacks since it sent troops to Somalia three years ago to help fight the Islamic militant group holding the country to ransom.

Al-Shabab was also blamed for the September 2013 attack on the Westgate shopping mall, which killed 77 people.