Several Kenyan police officers were killed in an attack Monday night by suspected Somali militants in the northeastern Garissa county, where 148 students were massacred last month, police said Tuesday.

Kenyan Officers Killed in Ambush

A police spokesman, George Kimoti, confirmed there was an attack in the Garissa region, and two security officials said many police officers had been killed in an al-Shabab ambush but could not give an exact death toll. The officials spoke on the condition of anonymity because they were not authorized to speak to reporters.

Kenya’s Daily Nation newspaper reported that at least 20 police officers were feared dead in the attack in Garissa’s Yumbis village.

The victims — who were on their way to rescue another team of officers wounded in an attack earlier on Monday — were moving in a convoy of four vehicles that the militants then burned. In the earlier attack, three police officers had been injured when their vehicle ran over a land mine, the officials said.

The same area was in the spotlight last week after suspected al-Shabab militants raided mosques and started to preach to congregations of Muslims. The militants reportedly hoisted flags before the security forces arrived. Kenya’s interior ministry said Friday it had “thwarted an attempted attack” on Thursday evening after the residents of Yumbis residents spotted armed militants in the area and alerted the authorities.

The Islamic extremist group al-Shabab has carried out several attacks in Kenya in retaliation for Kenya’s military involvement in Somalia, where Kenyan troops are part of an African Union force bolstering the Western-backed central government in Mogadishu.

Despite major setbacks in 2014, al-Shabab continues to wage an insurgency against Somalia’s government and remains a threat in the East African region.

The group claimed responsibility for a deadly assault last month on a college in Garissa town, as well as a 2013 assault on an upscale mall in the capital, Nairobi, in which at least 67 people were killed.

Kenyan officials are reportedly pondering the construction of a wall along the border with Somalia as part of the government’s efforts to stem the attacks.