PENTAGON — The United States is moving to fill the power vacuum in central Syria, worried the Islamic State terror group is looking to exploit the victory of Syrian rebels over forces loyal to former President Bashar al-Assad. U.S. warplanes Monday targeted IS camps and operatives in central Syria, marking at least the second time the U.S. has hit the terror group in areas formerly patrolled by Assad’s forces that had backing from Russian troops and airpower. U.S. Central Command, which oversees American forces in the Middle East, said the latest round of airstrikes targeted leaders, operatives and camps “in former regime and Russian-controlled areas.” The goal, CENTCOM said, is to ensure “pressure is maintained” against IS. CENTCOM and Pentagon officials said Monday initial assessments indicated the strikes killed12 IS members and that no civilians were killed or wounded. Neither CENTCOM nor the Pentagon offered additional details about the targets of Monday’s airstrikes or their operational value. The new strikes come just over a week after CENTCOM launched more than a dozen strikes against 75 IS targets in five locations across central Syria. Officials at the time said the targets included “a significant gathering of ISIS fighters and leaders.” Pentagon officials on Monday said the U.S. would carry out additional strikes as needed. “In as much as CENTCOM sees a potential threat posed by ISIS, and to mitigate their ability to be able to resurge, you’re going to see these strikes,” said Pentagon press secretary Major General Pat Ryder, using another acronym for the terror group. Until the collapse of the Assad regime, however, much of central Syria was a no-go zone for U.S. forces and their Syrian allies. “One of the big factors that has changed in Syria is the airspace,” Ryder told reporters Monday. “It previously had Syrian regime and Russian air defenses, which would preclude in many cases our ability to or desirability to go into those areas.” U.S. officials and independent analysts have long warned of a growing IS threat in areas of Syria under Assad’s control. A United Nations report issued earlier this year, based on intelligence from member states, warned the central Syria desert had become “a logistics and operations hub with 500 to 600 fighters.” More recently, U.S. officials warned that IS had been exploiting the lack of pressure from Syrian and Russian forces to plan attacks across the West. IS has “used a base of operations in central Syria to drive external plotting, turning this desert location into the current locus of plotting against the West, including the United States,” Brett Holmgren, acting director of the National Counterterrorism Center, said last month.