The mastermind of an attack that killed five Western oil industry workers, including two Americans, is a member of a Saudi opposition group in London, the Interior Ministry said Tuesday.

Mustafa Abdel-Qader Abed al-Ansari (search), a Saudi citizen wanted by security forces, was behind Saturday's attack on the offices of oil contractor ABB Lummus Global Inc., (search) in this industrial city, the ministry said in a statement carried by the official Saudi Press Agency.

Two Americans, two Britons and an Australian were among the dead, and dozens were wounded in the attack and ensuing police chase through the Red Sea city.

The attack, in which the body of one of the Americans was dragged behind the assailants' vehicle, prompted many Westerners to leave the kingdom.

Under the watch of armed guards, about 20 American ABB Lummus employees gathered at Yanbu's Holiday Inn on Tuesday to be shuttled to the airport. They refused to speak to reporters and details of their evacuation were not divulged, apparently for security reasons.

The ministry identified the other attackers — all Saudis — as Samir Suleiman al-Ansari and his brother Sammy Suleiman al-Ansari, and Ayman Abdel-Qader al-Ansari, Mustafa's brother. All were killed in the chase.

Saudi officials have blamed various interests for the attacks.

Interior Minister Prince Nayef said early Tuesday in Kuwait that Al Qaeda terror network was likely behind it. But his ministry's statement linked it to Saudi exiles in London and the Saudi Cabinet blamed only "external forces" interested in spreading chaos.

Crown Prince Abdullah also has blamed "Zionism" for being behind the attacks. And Foreign Minister Prince Saud, who made note of the lead assailant's connection to Saudi dissidents in London, said it is "well known" that the London dissidents "have contacts and are financed by parties that are linked to Israel."

The ministry statement said Mustafa al-Ansari left the kingdom in 1994 and was a member of a well-known Saudi opposition group, the London-based Committee for the Defense of the Legitimate Rights (search) in the kingdom, which advocates overthrowing the monarchy.

"He re-entered the country in an illegitimate way and infiltrated the borders to carry out despicable plans," the ministry statement said.

Saad al-Faqih, a founder of the opposition group, said Mustafa al-Ansari had briefly joined the organization at one time, but left it when the leadership split in 1996. He did not say how long al-Ansari was with the group.

"I remember the name. He was in the committee before the split," al-Faqih told The Associated Press in Cairo in a telephone interview from London. "Since then I haven't heard about him."

"I remember him as a very simple-minded person with little education," he said.

Al-Faqih split with Mohammed al-Masaari, another Saudi dissident who is still an Islamic activist in London. Al-Masaari did not answer telephone calls for comment.

Al-Ansari was about 22 when he came to London a decade ago after already spending time with Muslim fighters in Bosnia and Afghanistan, al-Masaari said. He was told he needed education and to learn to speak English.

"I found him simple, probably naive and lacking in political and knowledge of Islamic law," al-Masaari said. "He was enthusiastic for holy war and eager to go anywhere to fight ... but we told him that we are only active in political and religious (matters)."

Al-Masaari dismissed accusations of any Israeli connection to his group.

Muslim activists in London, speaking on condition of anonymity, told the AP that Scotland Yard had been pursuing Mustafa al-Ansari for years and that its agents had questioned many Muslim activists in the United Kingdom about him. Neither the British government nor Scotland Yard would confirm that.

The Saudi Press Agency also quoted an official government statement as saying "the Saudi Cabinet believes that an external force stands behind this deviated group and supports it with money and weapons."

"It (the external force) has a vested interest in spreading chaos all over the world," according to the statement issued after a Monday night Cabinet meeting chaired by Abdullah.

ABB Lummus said all 90 of its foreign employees in Yanbu were leaving. The first — all Europeans — left Monday night.

Many of the ABB Lummus employees leaving Tuesday had been among the Americans in Yanbu who attended a meeting with the U.S. ambassador the day before. Ambassador James C. Oberwetter later said he had encouraged Americans to leave the country.