Foreign fighters were involved in Sunday's bomb and gun attacks in Somalia's capital, Mogadishu, Prime Minister Abdi Farah Shirdon has said.
At least 29 people died in the suicide bombings at the main courts and near the airport, he said.
The al-Qaeda-linked al-Shabab group said it carried out the attacks.
African Union and government forces launched a major operation on Monday against the militants.
Local media reported that one of the suicide bombers was a Somali-Canadian, Mahad Ali Dhoore.
He had detonated a car bomb on a road near the heavily-fortified airport, the reports said.
The Somali government said nine gunmen had been involved in an earlier assault on the court.
Six of them detonated suicide vests, it said.
The bombing campaign was one of the worst in Mogadishu since al-Shabab lost control of the city in August 2011 to AU and government forces.
"Yesterday's [Sunday's] blasts eliminated the dreams of the puppet government," al-Shabab military operations spokesman Abdiasis Abu Musab told Reuters news agency by telephone.
The government was formed last year as part of a UN-backed peace process to end more than two decades of instability in Somalia.
Al-Shabab is fighting to create an Islamic state in Somalia.
Mr Shirdon said "several experienced" foreign fighters were among the attackers, but he did not identify their nationalities.
"We are concerned about the foreign involvement in this attack and this is why we are working so hard with our international partners on security and intelligence sharing," he said.
"Once again we see that terrorism is an international problem."
Mr Shirdon was speaking during a visit to the court complex and the Madina Hospital, where some of the wounded were being treated.
He said 58 people had been injured in the attack.
Seven of them were in a serious condition and the government was seeking "urgent advanced medical assistance" for them, added the prime minister.
AU troops and Somali forces blocked off streets and searched houses across the city on Monday to flush out suspected militants, Reuters reported.
Somali police official Mohamed Hassan told AFP news agency that more than 400 people had been detained.
"The operations are aimed at tackling insecurity," he is quoted as saying.
The AU has about 18,000 troops in Somalia to help the government battle the insurgents.
Al-Shabab was forced out of Mogadishu in August 2011 following an offensive by AU and government troops.
However, it has continued to carry out guerrilla attacks in the city.
The Islamist group still controls most villages and rural areas of southern and central Somalia.
This story initially said that there was a report in the local media that two Turkish aid workers had died in the explosion near the airport. Turkish diplomats have since told the BBC that none of their citizens died, though three Turkish people were wounded in the attack.