Algiers: Algeria’s army has killed four militants authorities believe were responsible for Friday’s attack on the Krechba gas facility operated by state oil company Sonatrach with BP and Statoil, a security source said on Sunday.

Al Qaida’s North Africa branch claimed responsibility for the rocket attack on the gas plant in central Algeria that caused no casualties or damage. BP had initially said the plant had been shut down as a safety precaution, but a top Sonatrach source said on Sunday that production was unaffected by the assault.

“Output in Krechba’s site was not affected, and Sonatrach’s CEO visited the gas facility to support workers and encourage them to maintain production,” the Sonatrach source said on condition of anonymity.

Algeria’s oil and gas facilities are heavily protected by the army, especially since Islamist militants killed 40 oil workers in an attack on the In Amenas gas plant near the Libyan border.

An Algerian security source who also did not want to be identified told Reuters that four militants were killed and three others wounded by the army in the desert region of Ain Saleh, where Krechba is located.

The Algerian defence ministry has not yet confirmed the operation.

The Krechba site produces 2 billion cubic metres of gas a year, and fields in the region of Ain Saleh produce around 9 billion cubic metres.

Al Qaida in the Islamic Maghreb has claimed several attacks across north and west Africa recently, including an assault on a resort in Ivory Coast last week that killed 18 people. The group said the attack was revenge for a French offensive against Islamist militants in the Sahel.

Algeria fought a bloody civil war in the 1990s that pitted government forces against Islamists and killed 200,000 people.

In recent years, the country has become an important partner in the Western campaign against Islamist militancy. The Opec nation is also a major gas supplier to Europe.