and the Norwegian company announced on Monday that they were withdrawing their employees from two of ’s largest fields after Islamic terrorists staged the second attack in three years on their installations.

In the assault, on Friday, a rocket-propelled grenade attack hit in Krechba, 750 miles south of Algiers. BP, a British company, and Statoil operate the installation jointly with the Algerian national oil company Sonatrach.

The did not result in damage or casualties, according to the companies, and production was interrupted only briefly. The Algerian Army rushed to secure the area, but the episode highlighted the difficulty it has in defending the country’s oil and gas fields, which stretch across a wide swath of the Sahara.

, Al Qaeda’s North Africa affiliate, claimed responsibility soon after the attack on In Salah, Algeria’s third-largest gas field. In an online statement, the group said the assault was part of its “war on the interests of the crusaders.” The group also suggested that it aimed to protect the environment and discourage shale gas exploration.

Three years ago, a splinter Qaeda group at In Amenas, not far from the Libyan border. The same three oil companies operate that facility. Forty people were killed during a four-day siege then, and damages were so heavy that one processing plant remains out of operation.

The latest attack was far more modest than the 2013 assault, staged by only a handful of terrorists armed with simple weaponry.

“It was a limited attack,” said Geoff D. Porter, head of , who is visiting Algeria. “It is a reflection of the limited capabilities that the group has in Algeria.” Nevertheless, Mr. Porter added: “It is going to have a dampening effect” on foreign investment.

Operations at both of the facilities from which BP and Statoil are withdrawing will be operated by Algerian personnel.

It was not immediately clear how long the two major European oil companies would keep their expatriate personnel, which together number several dozen, away from the facilities. But they indicated they were still committed to operating in Algeria, Africa’s largest natural gas producer and a primary source of energy for Europe.

“BP’s first priority is the safety and security of people,” the company said in a statement. It said the decision to conduct a “phased temporary relocation” “has been taken as a precautionary measure.” BP added that it would continue to support the ventures remotely.

After the 2013 In Amenas attack, the Algerian government instituted several new antiterrorism measures, including tougher security checks on local energy employees and wide-ranging air surveillance of the country’s oil and gas fields and installations.

Despite a long history of political violence, Algeria has been relatively peaceful in recent years compared with its neighbors, particularly Libya. But it has had difficulties attracting foreign investment to increase its sagging oil and natural gas production because of security concerns, corruption and investment laws that some companies find onerous.