Algeria's In Amenas field, where militants seized dozens of foreigners this week, is at the heart of an oil and gas region that has attracted international companies in recent years, partly because of its military-style security.

"For this group to have attacked there, in spite of tremendous security, is remarkable. Even as an Algerian, I need a special permit to go there," said Azzedine Layachi, an Algerian political scientist.

Events this week may change perceptions of an oil industry that has attracted billions of dollars in foreign investment since Algeria's government crushed an Islamist revolt during the 1990s.