At least 28 people were killed Saturday in an attack on a bus in Kenya’s Mandera county, authorities said. A group of over 100 armed men stopped the Nairobi-bound bus and ordered everyone out at around 5.30 a.m., Xinhua quoted Mandera Deputy County Commissioner Elvis Korir as saying.

“We were told that 100 armed men stopped the bus just after it left Arabia area and all the passengers were asked to come down and divided into two groups of Somalis and non-Somalis,” Korir said, adding the non-Somalis were sprayed with bullets. “We were also told that over 28 have been killed and many others injured, but we are yet to know the exact circumstances.

We are planning to dispatch a team of security personnel to the spot,” he said. Mandera County Police Commander Noah Mvivanda said initial reports indicated that the attackers were from the Al-Shabaab group from Somalia. He said the attack occurred at a place near the Kenya-Somalia border.

Mvivanda said the armed militants asked everyone on board to recite the Islamic doctrine and those who failed were shot dead. “Two young ladies who managed to escape said four police officers were among the dead, but we are yet to confirm,” Mvivanda said.

As Kenya sent troops across the border into Somalia in 2011, northern and parts of eastern Kenya have been hit by a series of blasts, with many targeting security forces and humanitarian workers.