( CNN ) -- Inadequate security measures and an unprepared military are two factors that allowed a group of Islamists to attack and take hostages at a gas field in Algeria in January , a report says . The report by Statoil , whose employees were among those taken hostage , says the companies that ran the gas field never anticipated a scenario where a large force of attackers hit the facility . The companies were too dependent on the Algerian military , which was `` not able to detect or prevent the attackers from reaching the site , '' the report says . At least 37 hostages were killed in the four-day ordeal . The plant is run by In Amenas Gas , a joint venture between oil giant BP , Statoil , and Sonatrach . Among the victims were five Statoil employees , which led the company to conduct an investigation into the circumstances surrounding the attack . `` The terror attack against In Amenas was an unprecedented attack , '' lead investigator Torgeir Hagen said in a statement . `` It clearly demonstrates that also companies like Statoil today face serious security threats . '' Algeria attack changes terror landscape in North Africa . The investigation team concluded that a different response to the attack would not have changed the outcome . But the lesson is that the site was not designed with security measures that would stop or slow an attack on that scale , the report says . The militant siege caught the world 's attention as it ensnared citizens from several nations and dragged on for days . Algerian authorities said they believe the attack was revenge for allowing France to use Algerian airspace for an offensive against Islamist militants in neighboring Mali . A group led by the jihadist commander known as `` Mr. Marlboro , '' Moktar Belmoktar , was responsible for the deadly attack . The plant in southern Algeria employed about 790 people , including 134 foreign workers . Algeria hostage crisis shows jihadists on rise .
An Algerian gas field was attacked in January . The site did n't have security measures that could have stopped the attack , report says . A different response would not have changed the outcome , says report from Statoil . At least 37 hostages were killed in the four-day ordeal .