RIYADH, May 27 (Reuters) - Saudi security services arrested a man suspected of helping al Qaeda-linked militants who shot dead four French tourists in February, an interior ministry spokesman said on Sunday.

The ministry identified the suspect as Majed al-Harbi, a prominent militant.

"The security forces have been following him," said the spokesman who asked not to be name. He said Harbi was arrested in the northern region of Hael. "There was no resistance during the operation."

The kingdom, a key U.S. ally, in April arrested eight other men in the same case and they remain in detention.

The main suspect in the attacks, Walled bin Mutliq al-Radadi, was killed earlier this month when police stormed a residential building in the Muslim holy city of Medina.

The Frenchmen, including a teenager, were killed by gunmen on Feb. 26 during a desert trip.

There was no claim of responsibility for the attack.

Islamic militants swearing allegiance to al Qaeda launched a violent campaign to topple the Saudi monarchy in 2003, carrying out suicide bomb attacks on foreign nationals and government installations, including the oil industry.

Tough security measures and a powerful publicity campaign helped crush the violence but analysts and diplomats have said the underlying currents of radical Islamic ideology and anger at Western policy in the region remain strong.

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