JERUSALEM (JTA) — A Palestinian resident of eastern Jerusalem was indicted for traveling to Syria to fight with the Islamic State, or ISIS.

Khalil Khalil, 25, was indicted Monday in Jerusalem District Court and charged with attempting to join an illegal organization, attempting to contact a foreign agent and illegally leaving the country.

In January he had told his family that he was going on the Hajj, a religious pilgrimage to Mecca, but instead flew with a friend to Turkey and then crossed the border into Syria, according to reports citing the Shin Bet security service. He was arrested on March 1 upon returning to Israel.

About 40 Palestinians and Arab-Israeli citizens have gone to fight with Islamist groups in Syria, The Jerusalem Post reported, citing the Shin Bet. The security agency is concerned that the fighters have “gained knowledge and experience of warfare and carrying out terrorist acts,” which “constitutes a serious threat of terror attacks within Israel’s borders.”