Somalia's Islamist Shebab militants killed at least 19 people when five gunmen detonated a bomb before storming a popular seaside restaurant in the capital Mogadishu, police said Friday.

"They killed nearly 20 people, including women and children," Somali police officer Mohamed Abdirahman said, describing it as a "barbaric and brutal attack against innocent civilians".

After a huge explosion, gunmen burst into the restaurant on Thursday evening as diners were sitting down for their evening meal.

The Al-Qaeda-linked Shebab have claimed responsibility for the attack, in which four of their gunmen were also killed, and one captured.