At least nine people have been killed including four attackers in an assault on Somalia's Criminal Investigation Department (CID).
Al-Shabaab claimed responsibility after two suicide car bombs struck the gates of the CID headquarters in Mogadishu before at least two gunmen stormed the building.
Ali Hassan, a police officer at the Central Investigations Department, said security forces foiled the assault and shot dead the gunmen who tried to storm the heavily fortified security facility.
Witnesses reported hearing two loud explosions before an exchange of gunfire, which lasted around half an hour.
The bodies of four civilians lay in the street near the compound, which was partially destroyed. A kiosk near the wall caught fire.
Al-Shabaab claimed responsibility for the bombing and shooting attack.
"A fighter rammed a suicide car bomb into CID then other armed fighters stormed inside. We are now fighting inside the CID building," Abdiasis Abu Musab, al-Shabaab's military operations spokesman, told Reuters.
Earlier this week, the Islamist group claimed responsibility for an attack on a hotel near Mogadishu's International Airport, which left at least 13 people dead.
Security analysts had warned the group could step up its attacks, taking advantage of the distraction caused by campaigning for a presidential election due in August.
Al-Shabaab, seeking to impose its strict view of Islam on the Horn of Africa nation, has also launched attacks in Kenya and Uganda, which have contributed troops to the African Union peacekeeping force.
Additional reporting by agencies
