Five Mauritanian Islamists have been arrested in connection with the murder of four French tourists, the public prosecutor in Nouakchott said Wednesday, amid speculation that terrorists were responsible for the killings.

Police on Wednesday were concentrating their search on three Islamists said to have defected to neighbouring Senegal.

Only on Tuesday, the French Foreign Ministry had countered speculation that the murderers might have had terrorist motives.

However, there was now widely-reported speculation that the crime may have been the work of al-Qaeda in the Islamic Maghreb - a Sunni Islamist militia which aims to overthrow the Algerian government and institute an Islamic state.

The group of holidaymakers consisted of a 73-year-old Frenchman, his two adult sons, his younger brother and a family friend.

The three attackers struck the five Frenchmen on Monday when they interrupted their car journey to Mali for a picnic break by the roadside near Aleg.

The attackers shot down their victims with automatic weapons. Earlier reports that the attackers had been after valuables proved false. The Nouakchott Info daily reported the bloodstained getaway car had been prepared with fake number plates.