At least four people, including three Syrian doctors believed to be aid workers, have been shot dead in an ambush near the Somalian capital, Mogadishu.
Another Syrian doctor was wounded in the attack, which took place on Wednesday as the group headed towards the town of Afgoye, 30 kilometres northwest of the capital.
Afgoye is a former stronghold of the al-Qaeda linked al-Shabab rebel fighters before they were driven out in May 2012.
A senior al-Shabab official, however, told AFP that the group did not carry out the attack.
Their fighters have often carried out shootings, bombings and suicide commando raids against government and international targets, including aid workers.
In August, the French aid organisation Doctors without Borders ended its two-decade presence in Somalia, ending all its operations because of increasing violence.
Al-Shabab were driven out of Somalia's major towns by a UN-mandated African Union force (AMISOM), but it still controls large parts of southern Somalia as well as pockets of Puntland.
On Monday, a new chief of the African Union force in Somalia took command, vowing he would lead the 17,700-strong force in a fresh offensive against al-Shabab, with more than 4,000 reinforcements expected.
Al-Shabab claimed responsibility for a bloody attack in September on a shopping mall in Nairobi in retaliation for Kenya's military intervention in Somalia.
Last week, 13 people were killed in four attacks in Kenya during week-long celebrations to mark the country's 50th anniversary of independence.
Source: Al Jazeera and agencies