Mogadishu, Somalia (CNN) The death toll from a double car bomb attack Saturday in Somalia's capital, Mogadishu, has risen to 15, a security official said.

Twenty others were injured, according to the official, Ibrahim Jama.

The blasts occurred in central Mogadishu, near the National Theatre, the presidential palace and the Daljirka Dahson monument. Plumes of smoke rose over the streets, and a heavy police presence was reported in the area.

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Al-Shabaab, a militant group linked to al Qaeda, claimed responsibility for the attacks in a statement posted on affiliated websites. A suicide bomber drove a car filled with explosives to the gate of the presidential palace and killed presidential guards, the statement said.

The mastermind behind the twin attack was detained by the country's National Intelligence Agency, officials said on Twitter.

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