Al-Shabab have claimed responsibility for a car bombing on Saturday that has killed at least three people and injured several more in Afgoye, northwest of Somalia's capital Mogadishu.

According to Somali officials, at least three people died and 20 others, including Turkish nationals, were injured, according to Turkey's state-owned Anadolu news agency. The AFP news agency reported that four people had been killed.

"The blast was huge, it destroyed a container used by the Turkish engineers who work on the Afgoye road construction," said witness Muhidin Yusuf.

"There were police who were guarding the Turkish engineers and several other people gathering near the checkpoint where the temporary shelter is located," said another witness Ahmed Said.

"I saw the dead bodies of several [people] and Turkish workers who were wounded in the blast."

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"The wounded are being treated at our Mogadishu Recep Tayyip Erdogan hospital. Two of our citizens are in a serious condition," Turkey's Health Minister Fahrettin Koca said on Twitter.

Anadolu said at least four Turkish employees of a construction firm were wounded and are being treated in hospital, citing information from the Turkish embassy in Mogadishu.

"A speeding suicide car bomb rammed into a place where the Turkish engineers and Somali police were having lunch," police officer Nur Ali told Reuters from Afgoye.

"So far, we know three Turkish engineers and their translator were injured," he said. "Two other policemen were injured in the blast."

Al-Shabab, which frequently carries out bombings to try to undermine Somalia's central government, which is backed by the United Nations and African Union peacekeeping troops, said it carried out the attack.

"We are behind the martyrdom of the suicide car bomb in Afgoye," Abdiasis Abu Musab, a spokesman for the group, said. "We targeted the Turkish men and the Somali forces with them. There are casualties of death and injuries."

'Huge blast'

Residents and police said al-Shabab fighters tried to mount an attack on Afgoye, about 30km from Mogadishu, late on Friday but were repulsed.

Local residents described a "huge blast" followed by "clouds of smoke".

"Before the blast, several Turkish engineers and well armed convoy of Somali police were at the scene," Farah Abdullahi, a shopkeeper, told Reuters from Afgoye.

"We see casualties being carried but we cannot make if they are dead or injured."

Turkey has been a major source of aid to Somalia following a famine in 2011 as Ankara seeks to increase its influence in the Horn of Africa to counter Gulf rivals like Saudi Arabia and the United Arab Emirates.

Turkish engineers are helping with road construction in Somalia.

A group of engineers was among those hit in late December in a blast at a checkpoint in Mogadishu that killed at least 90 people.

"We curse and condemn in the strongest terms the bomb terror attack which targeted innocent civilians in Somalia," the Turkish Defence Ministry said on its Twitter account.