Mauritanian authorities said they were searching Tuesday for three men suspected of links with a local terror network in connection with the fatal shooting of four picnicking French tourists.

Gunmen opened fire on the tourists after they refused to hand over their money Monday near Aleg, a small town 150 miles east of Mauritania's capital, Nouakchott, police said.

The dead included two children. Their father, the sole survivor, was seriously wounded and flown overnight to the main hospital in Senegal's capital, Dakar, where he was in an intensive care unit, said Moussa Samb, spokesman for the hospital.

Police said they detained one man suspected of arranging a taxi for the three attackers after the shooting. The driver told investigators that he took the men from Aleg to Boghe, a town on the Senegalese border about 40 miles to the south.

Police believe the three men then crossed into Senegal. Senegalese authorities in the region said they were aware of the case and were hunting for the men, but could not confirm their presence.

The three suspects were tried this year by a Mauritanian court on terror-related charges but acquitted and released. Prosecutors had accused them of being local members of the Algeria-based terror network, Al Qaeda in Islamic North Africa, and of training with the group in Algeria.

The man who allegedly arranged the taxi for the three was tried earlier this year on similar charges. He was convicted of having trained with the Al Qaeda group in Algeria and given a one-year suspended sentence.

Mohamed Ould Lemine, the police chief of Aleg, said Monday the French family withdrew a large sum of money before leaving the town on a sightseeing expedition. About seven miles outside the town, they stopped on the side of the highway to picnic; then the gunmen approached them demanding money. The family refused, and the attackers opened fire, Lemine said. The dead suffered bullet wounds to the chest and head, he said.

Afterward, the robbers sped off in an old model Mercedes-Benz, which police found abandoned several hours later, Lemine said. The men then took the taxi.

Such violence is rare in Mauritania, a relatively stable democracy in northwestern Africa perched on the far western rim of the Sahara desert.