An unknown number of people have been injured and others reportedly killed in the north-eastern Kenyan town of Elwak, which borders Somalia, in an explosive attack suspected to have been orchestrated by al Shabab militants, local media reported.

Police confirmed the explosion but said they did not have additional information, according to the privately owned The Star newspaper.

Details of the Monday morning attack are still sketchy, but state broadcaster KBC reported that an improvised explosive device that had been attached onto a donkey was detonated outside a police station in the town.

Several businesses in the town have halted operations.

Equity Bank, one of Kenya's largest lenders, said its branch in the town would remain closed awaiting "security agencies to advise on when operations can resume."

In recent months, al Shabab attacks have become more frequent in Mandera county, where Elwak is located.

Last month, a similar attack outside the Mandera police station killed at least three people, including police officers and a civilian.

Another police officer was killed and two injured after IEDs that had been planted on donkey carts exploded near the border crossing between the county and Somalia.