A man looks at a bus which was ambushed by gunmen in the Nyongoro area of Lamu county, near the Indian Ocean coast of Kenya…
FILE - A man looks at a bus which was ambushed by gunmen in the Nyongoro area of Lamu County, near the Indian Ocean coast of Kenya, Jan. 2, 2020.

NAIROBI - Four people were killed when suspected al-Shabab militants attacked a bus in northeast Kenya on Wednesday, a Kenyan security official told VOA. The Somali Islamist militant group has carried out numerous deadly attacks on buses and vehicles in the area as retaliation for Kenya's military presence in Somalia.

The bus was carrying passengers from Mandera County to Nairobi when it was attacked about midday, according to Onesmus Kyatha, Mandera's county commissioner.

"A bus ... was attacked between a place called Hola and Sraman, which is in Mandera North constituency," he said, "and the criminals are armed bandits, suspected criminals who sprayed the bus with bullets."

Mandera is bordered by Ethiopia to the north and Somalia to the east.

Kenya sent troops to Somalia in 2011 to fight al-Shabab alongside the African Union Mission in Somalia, with forces from at least six African countries.

In retaliation, al-Shabab militants have launched countless terror attacks in northeastern Kenya, along the Kenyan coast and in Nairobi in a bid to pressure Kenya to withdraw its troops from Somalia.

Kenya's security forces have heightened security in "terror prone areas," but this has not stopped the attacks.

Last month, al-Shabab attacked a joint U.S.-Kenyan base in Lamu County, killing three American military personnel.

Around Mandera, al-Shabab fighters have launched several fatal attacks. In July 2015, at least 14 people were killed and several others wounded in a gun attack near a military camp. The victims were workers from a local quarry.

Kyatha said the quick response by security personnel saved lives in Wednesday's attack.

"The police were able to move in fast from the nearby police unit based near those areas," he said. "They were able to move very fast on the ground and were able to secure the rest of the passengers, that is what I can confirm. The bus had about 35 passengers."

Al-Shabab's deadliest attack in Kenya came in April 2015, when gunmen stormed Garissa University and killed 148 people, most of them Kenyan students.