It was the most ambitious and the deadliest terror attack since the rampage by Pakistani militants through Mumbai five years ago. And it raises the alarming prospect that al Qaeda affiliates and other jihadist outfits could turn parts of northern and western Africa into no-go zones -- places too dangerous for Westerners to work, or even visit.

The attack on the In Amenas gas facility left 37 foreign workers dead, according to the Algerian prime minister. It showed that al Qaeda-linked groups now have the resources to reconnoiter and launch complex attacks against places far from their strongholds, using a network of camps and intermediaries throughout the desert.

If their rhetoric is to be believed, their goals include targets farther afield -- leveraging sympathizers among the vast North and West African diaspora in Europe.

A spokesman for the man who orchestrated the attack, Moktar Belmoktar, told French media Monday that France would see "dozens like Mohamed Merah and Khaled Kelkal." Merah shot dead seven people in Toulouse, France, last year; Kelkal carried out a series of attacks in France in 1995.

Oil companies reassess risk

The most immediate concern to counterterrorism analysts is that Belmoktar will launch more attacks against Western companies in North Africa. A second attack on oil and gas infrastructure could cause foreign oil companies to reassess their exposure in Algeria, Libya and parts of West Africa, or at least raise the security costs of doing business in the region.

A former head of intelligence for the Transitional National Council in Libya, Rami El Obeidi, told CNN last week that with the French intervention in Mali, "a Pandora's box has been opened," and he believes oil fields in Libya are also at high risk of being attacked.

Geoff Porter, a longtime observer of events in North Africa, says a mass exodus of Western companies from Algeria is highly unlikely. But, he said, "the Algerian hydrocarbons sector will enter a holding pattern for the next month or so, possibly resuming meaningful activity at the beginning of March."

"Companies looking at potential opportunities in Algeria will now look not only at the available acreage's prospectivity, but also how its location impacts security concerns and associated costs," Porter added.

Belmoktar, the leader of a newly formed Saharan al Qaeda franchise that split from al Qaeda in the Islamic Magrheb (AQIM) last fall, remains at large, likely hunkering down in northern Mali, where he is believed to have amassed weapons and a war chest of millions of dollars from ransom payments and smuggling.

Belmoktar has been based in or near the town of Gao, where endless tracts of desert as well as cave complexes have been a safe-haven for a variety of militant groups affiliated with al Qaeda since armed Islamist rebels drove out government forces early last year.

Last month he announced the formation of a new commando unit called Those Who Sign with Blood.

"He has all the resources he needs in terms of money, weapons and soldiers to launch new attacks, and his recruitment and fundraising efforts will likely be boosted significantly because of the attack," said Noman Benotman, himself a former Libyan jihadist who is now a senior analyst at the Quilliam Foundation in London.

Complex attack

Belmoktar became known as "Mr Marlboro" because of his smuggling enterprises. But Robert Fowler, a Canadian diplomat who was held for 130 days after being taken hostage by Belmoktar in 2008, said he had no doubts about where Belmoktar's priorities lay.

"His men were amongst the least materialistic I ever encountered. His criminality always served the expansion of jihad," he told CNN.

According to Benotman and other sources, the leader of the Algerian attack was Taher Ben Cheneb, the Algerian head of The Movement of Islamic Youth in the South. In his 50s, Cheneb was a longtime associate of Belmoktar. Cheneb was supported by Abdul Rahman al Nigeri, from Niger, and another Algerian, Abou al Barra.

The unit Belmoktar dispatched was well-armed: heavy machine guns, assault rifles, rocket-propelled grenades, mortars and explosives were recovered from the scene. And eyewitness accounts suggested the group or supporters had undertaken advance surveillance because it was apparent the attackers were familiar with the sprawling facility.

U.S. officials and North African sources believe the attackers entered Algeria from Libya and that some may have been trained in jihadist camps in southern Libya, not far from the In Amenas gas facility. The sources tell CNN that Libyan authorities are aware of three jihadist camps south of Sabha providing instruction to militants from North Africa and the Sahara, but have lacked the capability or will to move against them.

According to one source, Belmoktar visited the commandant of one of these camps on a trip he made to Libya in late 2011.

Benotman says the first phase of the assault involved an attempt to hijack a bus carrying Westerners as it traveled to the local airport. This would have required advance knowledge of travel arrangements. Benotman told CNN that in the view of regional security officials, the attackers likely received some insider help -- they also knew which units at the facility housed foreign workers.

Algerian Prime Minister Abdelmalek Sellal said Monday insider knowledge was passed on by a Niger national who had previously worked as a driver at the facility.

"If there was an 'inside man,' then this has certain implications for due diligence and vetting of employees at other oil and gas sites," according to Geoff Porter, who runs North Africa Risk Consulting Inc.

The attackers' plan, according to Benotman, was likely to take hostages from the bus across the nearby border into Libya, although he said it is possible their final destination could have been another neighboring country, such as Mali.

But the intervention of Algerian forces prevented their escape. The second part of the plan appears to have been to threaten to kill the workers if the Algerians tried to storm the complex.