MOGADISHU -- At least five people were killed and several others were injured on Sunday in twin car bomb blasts at the headquarters of Somalia's Criminal Investigations Department (CID) in the capital city of Mogadishu.

Police said the blasts hit the gate of the CID headquarters before militants stormed the building. Spontaneous gunfire could be heard.

The militant group Al-Shabaab has claimed responsibility for the attack. The group, fighting against the Somali government, frequently stages attacks in Mogadishu.

"There were two huge bombings near Somali's Criminal Investigations Department. I have seen black smoke rising from the place," Jamal Omar, an eye witness, told Xinhua.

The death toll could rise, Abdirashid Hamud, a police officer at the scene told Xinhua by phone. The CID headquarters is located alongside on a busy road.

Al-Shabaab, which literally means "The Youth" or "The Youngsters" in Arabic, is a terrorist group based in East Africa. The militant group battles with the UN-backed government in Somalia, and has carried out a string of attacks in neighboring Kenya.

Allied to al-Qaeda, the group has been pushed out of most of the main towns it once controlled, but it remains a potent threat to peace and stability in the region.