Radicals from Libya’s Islamic State affiliate abducted nine foreigners, including four Filipinos, in an attack on a central oil field last week, and beheaded eight Libyan guards, officials said Monday.

The attack last Friday on the al-Ghani oil field near the town of Zalla, some 750 kilometers (470 miles) southeast of the capital, Tripoli, was part of a series of deadly assaults on Libya’s oil lucrative infrastructure by the Islamic State group.

The attacks in recent weeks have forced Libya to declare 11 fields non-operational, including al-Ghani, and invoke a force majeure clause that exempts the state from contractual obligations.

Libya’s military spokesman, Ahmed al-Mesmari, warned on Monday that Islamic State radicals’ long-term goal is to take over Libya’s petroleum industry. “This is the lifeline of the Libyan people,” he said, adding the consequences of such a loss would be dire.

During the attack on al-Ghani, an employee watched the beheadings of the eight oil guards and subsequently died of a heart attack, al-Mesmari also said. He not elaborate on how the army knew about the beheadings but the force serving as oil guards is closely allied to the Libyan military, which answers to the eastern-based government, one of Libya’s two rival governments.

Meanwhile, authorities in the Philippines said four of their nationals were among the nine abducted from the oil field. An Austrian, a Czech, a Bangladeshi and a Ghana national were also taken. One hostage remains unidentified.

Department of Foreign Affairs spokesman Charles Jose said Manila was working with the employer of the nine, Austrian-owned VAOS Oil Service, the Libyan government and embassies of the other foreigners abducted.

The incident brings the total number of Filipinos missing in Libya to seven. Three others were snatched in another oil field on Feb. 3 and their whereabouts also remain unknown.

Jose also appealed to around 4,000 Filipinos still in Libya to get in touch with the Philippine embassy and avail of the government’s mandatory repatriation program which covers the cost of travel back to the Philippines.

The Al-Ghani oil field had suspended operation for two weeks prior to the attack and most of the workers had left by the time the gunmen arrived there, he added. On Sunday, Philippine diplomats met with 52 other Filipino employees of VAOS Oil at the company’s headquarters in Tripoli. Jose said 36 of the 52 Filipinos have said they want to go home and more are expected to sign up for repatriation in the coming days.

The Philippines is among the world’s top labor exporters with about a tenth of its 100 million people working abroad

Three years after Libyan dictator Moammar Gadhafi was overthrown in an Arab Spring-inspired uprising, Libya is bitterly divided between two rival governments and a wide array of militias. The internationally recognized government and parliament were forced to relocate to the country’s far east after Tripoli fell to allied militias last summer.

Al-Mesmari, the Libyan army spokesman, said that following the attack on al-Ghani, fighter jets took off from the Ras Lanouf port on Libya central coastline and targeted the radicals. Earlier, Tripoli-based militias said their own fighter jets tried to stop the attack on al-Ghani but failed.

The Libyan turmoil has provided fertile ground for radicals allied with the Islamic State group, which is fighting in Iraq and Syria to expand its self-styled caliphate. The Libyan IS affiliate now controls the eastern city of Darna and also Sirte, and has carried out several deadly suicide bombings across the country.

In January, radicals from Libya’s IS affiliate stormed a luxury hotel in Tripoli, and in February, they released a video showing the beheading of 21 captured Egyptian Christians. The Egyptian military launched airstrikes on Darna in retaliation for the horrific slayings. SAPA