evidence: Islamic State infiltration into Lebanon has highlighted challenges facing the LAF. In 2013, fighting in the Qalamoun mountain region between Syria and Lebanon transformed the Lebanese border town of Arsal into a rear base for Syrian armed groups.25 In August 2014, clashes broke out between the LAF and Islamic State/Nusra Front militants in Arsal. Nineteen LAF personnel and 40 to 45 Lebanese and Syrians were killed, and 29 LAF and Internal Security Forces were taken hostage.26 It was generally believed that nine of the hostages were still being held by the Islamic State, until the location of their remains was disclosed as part of an August 2017 cease-fire arrangement with the group. U.S. officials described the August 2014 clashes between the Islamic State and the LAF in Arsal as a watershed moment for U.S. policy toward Lebanon, accelerating the provision of equipment and training to the LAF.27 The situation in Arsal is compounded by the refugee crisis—the border town hosts more than 40,000 refugees, exceeding the Lebanese host population by more than 15%.28 [...] Both the LAF and Hezbollah have deployed forces at various points along Lebanon's eastern border to prevent the infiltration of militants from Syria. In May 2017, Hezbollah withdrew from a 67 km area stretching from the Masnaa border crossing with Syria (the primary official land crossing between the two countries) to Arsal, and was replaced by LAF forces.37 Hezbollah leader Hasan Nasrallah called on HTS militants to leave Arsal, suggesting that Hezbollah could take military action if needed. However, some Lebanese politicians argued that the job of clearing militants from Arsal should rest with the Lebanese government alone.38