Story highlights The attack opens with the explosion of a suicide car bomb

More explosions follow, and gunmen storm the hotel

Many civilians die, says an official present at the hotel

Mogadishu, Somalia (CNN) Gunmen stormed a popular hotel in Mogadishu on Sunday after opening their attack with multiple blasts, Somali officials said.

At least 15 people were killed, medical and police officials said. Islamist militant group al-Shabaab, an al-Qaeda affiliate, claimed responsibility for the attack via a Somali radio station run by the group.

Many of the dead were civilians, said interior ministry spokesman Mohamed Yusuf Osman, who was at the attack site, the Sahafi Hotel. The armed men pushed inside the building, then Somali special forces deployed to fight the militants.

The attack kicked off when a suicide car bomb exploded at the gates of the hotel, which government officials use as a residence, Osman said.

An intelligence service official, who did not want to be named, said that two more explosions detonated during the attack -- one believed to be a bomb remotely targeting first responders. The third explosion was believed to be carried out by a suicide attacker.

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