The Philippines is investigating the involvement of Filipino militants in the three-year civil war in Syria after two locals were reported killed fighting for ISIS terrorist group, an intelligence official said on Saturday. A senior police intelligence official said Manila was also monitoring young Filipino Islamists who have gone to Syria and Iraq, and then tried to radicalize others on their return home. The Philippines has been battling its own small but violent militant group, Abu Sayyaf, which has been blamed for kidnappings, beheadings and bombings in the south. Since 2002, a U.S. special forces unit has been advising and training local troops. Thousands of fighters from dozens of countries have traveled to Syria and Iraq to fight with extremist groups, prompting the United States to draft a U.N. Security Council resolution demanding countries "prevent and suppress" the recruitment and travel of foreign fighters. "These are disturbing developments that could affect our internal security situation," the intelligence official, who declined to be named because he was not allowed to talk to the press, told Reuters. "We have scant data based on intermittent information made available from different agencies, including the Department of Foreign Affairs. We are now exchanging intelligence with our foreign partners so we can build our own data base." Based on these exchanges, he said they have noted a gradual increase of foreign fighters heading to Syria coming from Indonesia, Malaysia, the Philippines, Thailand, and Xinjiang, a troubled province in western China. But the movement is not only one way, he said. Some locals who saw action in Syria, labeled themselves as "veterans" had returned to the south of the mainly Catholic state to spread extremist ideologies. Rommel Banlaoi of the Center for Intelligence and National Security Studies said the threats from ISIS militants in the Philippines "is real rather than imagined". "ISIS is replacing al-Qaeda as the champion of the world Islamic caliphate," Banlaoi said, adding a video on YouTube last month indicated an Islamic caliphate in the Philippines has been established. Militants from Abu Sayyaf, Khilafa Islamiyah Mindanao, Bangsamoro Islamic Freedom Fighters and the Muslim convert group Rajah Solaiman Islamic Movement had pledged support to ISIS militants in Syria and Iraq. On Wednesday, Washington authorized airstrikes for the first time in Syria and more attacks in Iraq in a broad escalation of a campaign against the ISIS, which has seized large stretches of Iraq and Syria.