Officials say the bomber was his own teenage niece, who had joined the Islamist militant group al-Shabab.
The group said it carried out the attack and said more would follow.
Meanwhile, two people are said to have been killed in Mogadishu during protests against a deal to extend the terms of the president and parliament.
Under the deal signed in Uganda on June 9, their mandates have been extended until June 2012 and the prime minister is to be sacked.
June 10 saw a second day of demonstrations in support of Prime Minister Mohamed Abdullahi Farmajo.
Witnesses said troops fired on the protesters, who had gathered outside the hotel where MPs have been meeting.
The attack against Sheikh Hassan was the third suicide attack in Mogadishu in three weeks.
(VOV)
