A number of police officers have lost their lives in an overnight ambush by Somalia-based al-Shabab militants in the Kenyan city of Garissa, close to the border with Somalia, sources say.

There are conflicting reports about the number of the casualties in the Monday night raid, with various sources reporting figures between 10 and 25.

“The area is on the remote side of [the town of] Garissa not far from the border, that is why we are having a problem getting information instantly,” a local police officer said on Tuesday.

Meanwhile, police spokesman George Kinoti also said 13 police officers have gone missing following the overnight ambush.

“More police officers have been dispatched to look for those missing and the attackers,” he added.

The Kenyan border city has witnessed numerous attacks by militants from the al-Shabab terror group since last month.

In the deadliest incident, al-Shabab carried out an attack against the Garissa University College campus on April 2, killing nearly 150 and injuring 79 others. The attack ended after Kenyan security forces killed all the four attackers who had taken hundreds of students hostage.

Kenya currently has over 3,000 soldiers stationed in southern Somalia, where they have been battling al-Shabab. The country sent troops into Somalia in late 2011, after the militant group carried out a series of raids inside Kenya.

Somalia has been the scene of clashes between government forces and al-Shabab militants since 2006.

The militants have been pushed out of the Somali capital, Mogadishu, and other major cities in the country by the African Union Mission in Somalia, which is largely made up of troops from Ethiopia, Uganda, Burundi, Djibouti, Sierra Leone and Kenya.

Al-Shabab members have, however, continued to carry out attacks in Mogadishu despite being ousted from their bases in the seaside city in 2011.