A suicide bomber has attacked a government office in the somali capital, Mogadishu, causing a nearby school to collapse, police say.The car bomb in Howlwadag district killed three soldiers and injured 14 people, including six children. The blast also damaged nearby houses and blew the roof off a mosque .The militant group Al-Shabab, which has waged an insurgency for more than 10 years, said it carried out the attack.