Approximately 50 foreign ISIS fighters have been captured in Syria and Iraq since the start of November, a US military official told CNN on Tuesday. The official added that some of the fighters were captured as they were attempting to hide in civilian vehicles and were discovered by either the US-backed Syrian Democratic Forces or Iraqi Security Forces. The ISIS operatives came from several countries in the Middle East, Europe, Africa and Southeast Asia, the official said. The chairman of the Joint Chiefs of Staff, Gen. Joseph Dunford, said in October that “as many as 40,000 foreign fighters from 120 different countries” had joined ISIS in Iraq and Syria, when he spoke to reporters following a chiefs of defense conference at Fort Belvoir, Virginia. Officials have said that a central tenet of the Trump administration’s strategy for fighting ISIS is preventing these foreign fighters from returning to their countries of origin to carry out attacks. A US defense official told CNN last week that as part of an effort to facilitate an ISIS resurgence, the terror organization is establishing small sub-organizations in ungoverned areas like Afghanistan, Libya and Yemen in the hopes of helping foreign fighters cross borders and link up with other ISIS branches outside Iraq and Syria. Dunford said his counterpart from the Philippines had told him that 30 fighters had returned there from ISIS territory in Syria and Iraq. “Foreign-fighter flows into Syria have nearly stopped,” Brett McGurk, the special presidential envoy for the fight against ISIS, said while appearing alongside Dunford in October, adding that “foreign fighters are unable to get out of Syria.” US Army Col. Ryan Dillon, a spokesman for the US-led coalition, told reporters last month that four such foreign fighters had been captured by the Syrian Democratic Forces in October while trying to escape Raqqa by hiding among civilians who were being evacuated as part of a local deal aimed at preventing casualties. While some reports alleged that several foreign fighters managed to escape Raqqa despite the screening, the coalition maintains that it has seen no indication of that. The US-led coalition estimates that fewer than 3,000 ISIS fighters remain in Syria and Iraq, largely confined to more remote areas after having been driven out of major urban areas. And while Iraqi Prime Minister Haider al-Abadi announced Saturday that Iraqi forces had restored control over the entire border with Syria and defeated ISIS, mop-up operations continue. That same day, two UK Royal Air Force Tornado jets carried out a coalition airstrike against a group of ISIS fighters in a remote area some 40 miles northwest of Tikrit, according to the UK Ministry of Defense. From Friday to Sunday the US-led coalition also carried out 13 strikes against ISIS in Syria.