(Adds operations continuing, news conference)

By Vincent Fertey

NOUAKCHOTT, April 30 (Reuters) - Mauritanian security forces captured eight suspected al Qaeda militants on Wednesday, including a fugitive accused of killing four French tourists, the chief prosecutor said.

The Dec. 24 killing of the French tourists and a shooting attack on the Israeli embassy in Mauritania's capital Nouakchott in February raised fears of a rise in Islamic militant violence in the traditionally sleepy Saharan state.

Those arrested included Sidi Ould Sidna, a suspect in the slaying of the French tourists, whose escape from police custody outside a courtroom on April 2 led to a nationwide manhunt and a series of raids on suspected militant hideouts.

Chief prosecutor Mohamed Abadllahi Ould Tiyib told Reuters Sidna was detained with another suspect, Khadim Ould Semane, who is accused of masterminding the Israeli embassy attack.

"The two most important suspects have been arrested. I have seen them. They are in detention at the gendarmerie," he said.

Four of those arrested were being actively sought for their alleged role in the attacks while the others were suspected of helping them evade arrest, Tiyib told a news conference later.

Security sources said Wednesday's raid took place without a shot being fired. Police operations including searches continued across the Atlantic coast city until late in the day.

Mauritania is one of the few Islamic countries that has officially recognised Israel.

ON THE RUN

Sidna's escape had been an embarrassment to the authorities and raised questions over their ability to counter Islamic militancy and insecurity across the Saharan region.

Government security services responded with a series of raids, rounding up al Qaeda suspects including one man accused of involvement in the tourists' killing who tried to escape dressed as a woman with a Muslim veil over his face.

A policeman and a suspect were killed in one shootout.

Semane had been on the run for more than a year. He was convicted in absentia in June 2007 in a mass trial of more than 20 people suspected of trying to set up a pro-al Qaeda group.

Most of the defendants in that trial were acquitted, but Semane was convicted of possessing illegal arms and false documents and sentenced to two years.

The spate of attacks since December, claimed by North Africa's al Qaeda in the Islamic Maghreb, triggered concerns the group was extending its operations into Mauritania from its established bases in neighbouring Algeria and nearby Morocco.

Within days of the killing of the French as they picnicked by a roadside in southern Mauritania, al Qaeda claimed responsibility for an attack on a remote northern army post in which several Mauritanian soldiers were killed.

The attacks prompted the first cancellation of the Dakar rally after French officials said al Qaeda had made direct threats against the French-organised trans-Saharan motor race.

Mauritania is a mostly arid country which exports iron ore, fish and a small amount of crude oil but little else. Tourism is an important source of hard currency. (Additional reporting by Ibrahima Sylla and Noiselle Champagne; writing by Alistair Thomson; Editing by Pascal Fletcher)

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