Three ministers were among those killed in the attack at a graduation ceremony for medical students in Mogadishu on Thursday.
Attacker 'wore disguise'
A suicide bomber disguised as a woman carried out the attack at the Shamo hotel, Dahir Mohamud Gelle, the Somali information minister, said.
A security official told the AFP news agency most of the dead were believed to be students.
Of the three ministers killed in the blast, one was a woman - Qamar Aden Ali, the health minister.
Ibrahim Hassan Adow, the minister for higher education, and Ahmed Abdullahi Wayel, the minister for education, also died.
Also among the dead were two journalists and two professors. More than 40 people were wounded in the attack.
Mohammed Ali Nur, the Somali ambassador to Kenya, told Al Jazeera: "What we understand is that someone blew himself up at the ceremony and the attack aimed to target government officials. We appeal to the international community to help our country in this time of need," he said.
Rashid Abdi, a political analyst, told Al Jazeera from Kenya that despite al-Shabab's denial of responsibility, a faction within the organisation could have carried out the attack without the knowledge of the rest of the group.
"This may have been a strategic mistake for them because civilians were casualties. There was a great deal of revulsion by the public, and the pictures coming out of Mogadishu have shocked many Somalis," he said.
"I think that is why al-Shabab may have rushed out a media statement saying they are not involved - because this will seriously undermine their credibility."
The UN Security Council condemned the attack, while calling on groups in Somalia opposed to the transitional government to disarm immediately.
A statement approved late on Thursday by all 15 council members said that it supported the Somali people "in their quest for peace and reconciliation" and the UN-backed government "as the legitimate authority in Somalia".
|Witnesses said the suicide attack appeared to have targeted government officials [Reuters]
The African Union (AU) said that the "inhumane and cowardly attack would not deter the resolve and determination of the African Union to support the people of Somalia in their quest for peace and reconciliation".
Catherine Ashton, the EU foreign policy chief, said in a statement: "I condemn in the strongest possible terms this cowardly attack against civilians including students, doctors and journalists."
Ashton also assured the transitional Somali government of the "EU's determination and commitment to support its efforts to fight extremism and reconstruct a peaceful Somalia".
Al-Shabab and other anti-government groups regularly attack government troops and AU peacekeepers, in efforts to force them out of the country.
Al-Shabab and allied groups control much of southern and central Somalia and want to impose their version of sharia, or Islamic law, in the country.
Somalia has not had an effective government since 1991, when Mohamed Siad Barre was overthrown by armed groups who then turned on each other.