UPDATE 2-Islamic State kills four security personnel in Syria, state news agency says

(Adds new attack in paragraphs 5-6) CAIRO, Feb 23 (Reuters) -

Islamic State militants ​killed four Syrian government security personnel in ​northern Syria on Monday, the ‌Syrian state news ​agency reported, in what would be the group's deadliest attack on government forces since the ouster of President Bashar al-Assad. The assault on ‌a checkpoint west of Raqqa city underlined an escalation in attacks by the jihadist group against President Ahmed al-Sharaa's government, two days after the jihadist group declared "a new phase of operations" against it. Islamic State ‌issued no immediate claim of responsibility for Monday's attack. On Saturday, the group claimed two ‌attacks targeting Syrian army personnel in northern and eastern Syria, in which a Syrian soldier and a civilian were killed.

The Syrian state news agency said forces foiled Monday's attack and killed one of the militants. It quoted a ⁠security source as ​saying Islamic State carried ⁠out the attack. Separately, one soldier was killed after unknown gunmen attacked the army headquarters in the city of Mayadin ⁠in Deir al-Zor in eastern Syria, the Syrian state news agency reported on the early hours of Tuesday. There ​was no immediate claim of responsibility for the attack, which occurred in the same city ⁠where the Islamic State carried out an attack days earlier.

The Syrian government joined the U.S.-led coalition to combat Islamic State ⁠last ​year. In January, government forces seized control of Raqqa from the Kurdish-led Syrian Democratic Forces, along with much of the surrounding territory in northern and eastern Syria. Meanwhile, U.S. forces on Monday ⁠began withdrawing from their largest military base in the northeast, according to three Syrian military and security ⁠sources - part of a ⁠broader pullout of U.S. troops who deployed to Syria a decade ago to fight Islamic State.