Algiers - Jihadists launched a rocket attack on Friday on an Algerian gas plant jointly operated by foreign companies, three years after a deadly hostage crisis at another facility in the Sahara desert.It was the most serious such attack since the 2013 assault, when Islamist militants stormed a complex in Algeria's remote east and began a four-day siege that left dozens dead.There were no reports of casualties in Friday's attack, companies and workers at the site said."This morning, at approximately 06:00 local time, the In Salah gas asset in Krechba was hit by explosive munitions fired from a distance," Norwegian oil and gas firm Statoil said in a statement.Britain's BP, which along with Algerian company Sonatrach also operates the plant 1 300km south of Algiers, said no employees were hurt."There are no reports of any injuries to personnel at the site and the Central Processing Facility (CPF) has been shut down as a safety precaution," it said. A plant employee who did not wish to be named told AFP that the site is surrounded by a security fence and soldiers are permanently on guard."The rockets seem to have been fired from very far away," he said.Military personnel mobilised soon after the rocket fire to prevent the jihadists gaining access to the facility, the employee added. Jihadist attacksNo group claimed immediate responsibility for Friday's attack and Algerian authorities could not provide further details.In 2013 a four-day siege and two rescue attempts by the Algerian army at a gas facility at In Amenas resulted in the deaths of 38 hostages, all but one of them foreigners.That site is also jointly run by Sonatrach, BP and Statoil.A group allied with Al-Qaeda claimed responsibility for that attack, which prompted a widespread security review in the North African country, heavily reliant on income from gas exports.The head of Algeria's army last week called for increased vigilance following what he termed an "unprecedented deterioration" in security.Algeria has been on guard against jihadist attacks such as those experienced by its neighbours Libya and Tunisia, with local press reporting the deployment of tens of thousands of soldiers along its vast desert borders. On Monday, a security source said a militant leader who had joined the Islamic State group was killed during an army operation west of Algiers.A brutal civil war in the 1990s between the government and Islamists killed 200 000 people.Despite adopting a peace and reconciliation charter in 2005 aimed at turning the page on the conflict, armed groups remain active in the centre and east of Algeria.A total of "157 terrorists, including 10 commanders" were killed or arrested in military operations last year, according to the defence ministry.Algeria, a member of the OPEC oil cartel, is one of the world's largest exporters of natural gas, with revenue from fossil fuels accounting for 95 percent of its exports.It has an estimated 16 billion cubic metres of conventional gas and 20 million cubic metres of non-conventional gas, according to Sonatrach figures.