At least three people were killed when a suicide attacker set off a car bomb at a checkpoint outside the main base of an African Union peacekeeping force in the Somali capital on Monday, police said.
There was no immediate claim of responsibility.
Islamist al Shabaab militants, who want to topple the Western-backed government, have carried out similar attacks in the past.
“So far we know three of the security forces died. We believe al Shabaab is behind the attack,” Mohamed Ahmed, a police officer, told Reuters.
He said the death toll was likely to go up because the bomb was powerful and it had caused damage even to nearby residential buildings.