The Madain Saleh killings were the first of foreigners since 2004

Saudi sources told the BBC police were treating Monday's ambush as terrorist- related, the first deadly attack on foreigners in nearly three years.

The identities of the dead - all French nationals - have not been released.

Gunmen opened fire on their car near Madain Saleh, a remote archaeological site popular with tourists.

A doctor who treated the teenager said he was son of a Moroccan-born mother.

"He died from the consequences of his shoulder injury. Part of the bullet was still there. He was bleeding. We carried out an operation but it was no good. He died this morning," said Dr Metwakkil Hajjaj, in quotes reported by Reuters.

The other dead are thought to be French expatriates working in Saudi Arabia.

The road where the attack occurred is reported to be restricted to Muslims only, as it leads to the Islamic holy city of Medina.

However, a French diplomat quoted by the French news agency AFP said that three of those shot dead were not Muslims.

The French foreign ministry said two of the victims were employees of the electrical equipment manufacturer Schneider Electric, and one was a teacher.

SAUDI ATTACKS ON FOREIGNERS May 2003: Suicide bombers in Riyadh kill 35 people May 2004: 22 civilians die in Khobar compound shootout June 2004: Gunmen kill BBC cameraman Simon Cumbers and seriously injure correspondent Frank Gardner June 2004: US contractor Paul Johnson beheaded No fatal attacks since 2004

Saudi Arabia has been waging an intense campaign against militants linked to al-Qaeda since a wave of suicide attacks on foreigners in 2003.

Some women and children were also part of the group, but were not hurt, a Saudi official said.

French President Jacques Chirac described the attack as "hateful".

"I condemn with the utmost strength this horrible act," he said, promising to lend all support to the Saudi authorities in bringing the perpetrators to justice.