At least two people were killed and 20 wounded when a group of Turkish contractors were target by a suicide car bombing at a construction site along a highway outside Somalia's capital, police said on Saturday.

Six Turkish nationals were among the wounded, with two in serious condition, Turkish Health Minister Fahrettin Koca said.

The Turkish construction workers appeared to be the bomber's target, Somali police Col. Abdi Abdullahi said.

"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. Two other policemen were injured in the blast," Ali said later when asked about casualties.

Turkey's state-owned Anadolu news agency said four Turks, employees of a construction firm, who were wounded in the attack and were being treated in hospital, citing information from the Turkish embassy in Mogadishu.

This comes three weeks after an Islamist group, Al-Shabaab claimed responsibility through an audio message, for a car bomb blast in Mogadishu that killed at least 90 people in late December.

Two Turkish nationals were killed when a small team of Turkish engineers were present at the time of the blast constructing a road to the city.

The bombing was the deadliest the country had experienced in more than two years with nearly three decades of Islamist violence and clan warfare.