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Suspected Islamic State militants attacked a small town in central Libya on Monday, killing at least four people, including the mayor's son and two policemen, and torching the local police station, according to residents and a lawmaker from the area.

The attack on al-Fuqaha began around 1 a.m. At least a dozen townspeople have gone missing, presumed abducted by the militants, including an 80-year-old man, said Ismail al-Shareef, a lawmaker from the area.

The militants torched the town's police station along with two houses, residents said, speaking on condition of anonymity for fear of reprisals.

The attack on al-Fuqaha, south of the former IS bastion of Sirte on the Mediterranean coast, underlines the volatility of Libya's central region, where IS and other armed groups, including some from neighboring Chad, operate as highway robbers or attack patrols of the self-styled Libyan National Army led by Gen. Khalifa Hifter.

Following the attack, Hifter's forces, which answer to the government based in eastern Libya, pursued the attackers into the desert, according to al-Shareef. He said he believed the attack was retaliation for recent LNA operations against IS militants in the area and the capture of senior leaders of the militant group.

The U.N. mission in Libya condemned the attack and said two of the four killed by the militants were "executed in public." It did not say how they were killed, but residents had earlier said they had their throats slit. It said in a statement that It was "deeply concerned" about what it called the increasingly fragile security situation in central Libya.

Libya plunged into chaos after the 2011 uprising that ousted and killed longtime dictator Moammar Gadhafi and is now governed by rival administrations in the east and west. It has also become a haven for armed groups, including several from neighboring countries, which survive on looting and human trafficking.

The LNA drove IS from Sirte in 2016 and from Derna, another stronghold of the extremists, earlier this year. However, the militants have found refuge in the vast deserts of central and southern Libya, where they continue to stage attacks.