NAIROBI, Kenya (AP) — The owner of a bus company says three people have been killed by suspected extremists from Somalia after they were pulled out of a bus in northeastern Kenya.

Haji Abass said Wednesday that the bus belonging to his company, Moyale Raha, was heading to the Kenyan capital of Nairobi from Moyale, a market town on the Ethiopian border in Mandera county, when it was attacked.

Abass said suspected al-Shabab fighters in full police uniform flagged the bus down, but the conductor and passengers who knew the route said there was no police roadblock in the area, so the driver kept going.

The fighters then fired at the bus, injuring the driver. The front and back tires deflated and the bus lost control and went into a ditch.

The fighters then pulled out the passengers and killed two non-Muslims, as in previous attacks, as well as one Muslim, Abass said. It was not clear why they shot a man believed to be Muslim, he said.

The al-Qaida-linked al-Shabab has vowed retribution for Kenya’s troop presence in neighboring Somalia. Its fighters have carried out numerous attacks on Kenyan soil since Kenya deployed troops in 2011 to fight the extremists.

Such attacks have brought education to a near-standstill in Kenya’s Mandera, Garissa and Wajir counties. Nearly 1,000 non-teaching staff were withdrawn from the counties that border Somalia after three Kenyan teachers were killed in Garissa last month.