A Muslim Israeli citizen who has reportedly joined the Islamic State group in Syria completed a full service as an IDF combat soldier and has barely had contact with his family for the past five years.

The man’s family members and neighbors told The Times of Israel of a brilliant high school student whose family had high hopes for his future.

But following an argument with his father, Riyad, the man left the family home and joined the IDF, where he served as an infantryman in the Givati Brigade.

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His mother, Miasara, told The Times of Israel that she hasn’t been in contact with her son for five years and doesn’t know where he is.

Identified only by the initials H.B., the man is 25 years old and a resident of a village in northern Israel, Arab intelligence sources told The Times of Israel last week.

He traveled from Israel to Turkey and then crossed the border into Syria, where he joined the ranks of IS.

According to the man’s uncle, he completed a full military service in the IDF — usually a three-year stint. During weekend furloughs he would return in full IDF uniform but, due to the continuing feud with his family, stay at vacation resorts in the area of his home village, paying his way by doing guard duty.

At one stage, his uncle managed to resolve the dispute with his father, who objected to his son serving in the Israeli army.

After completing army service, however, his movements became unclear. The uncle managed to find him work at a prominent Israeli security company for a while, but little is known of his whereabouts for most of the intervening period, until he left for Syria.

According to his military identification card, which was seen by a Times of Israel reporter, he was slated to have completed his military service in January 2014.

It wasn’t immediately clear when the man traveled to Syria, where he crossed the border, or his current whereabouts.

Soldiers from Givati, one of the original brigades of the IDF, include Hadar Goldin, who was killed in the 2014 Gaza conflict and whose body is in Hamas possession, and Eldad Regev, whose body was returned to Israel as part of a 2008 prisoner swap, two years after he and Ehud Goldwasser were abducted by Hezbollah.

Last month, Israel security services arrested five men from the northern city of Jaljuliya, charging them with attempting to join IS in Syria. A relative of one of the men made headlines in October when he flew a paraglider into southern Syria from the Golan heights to join jihadists fighting there.

Arab intelligence sources told The Times of Israel that between 100 and 150 Israeli Arabs are either fighting for or have been detained by the Islamic State, but this is the first case involving an IDF veteran.

In March, East Jerusalemite Muhammad Musallam, who had gone to Syria join IS, was executed after the group claimed he was a Mossad agent. A video of the execution released by the jihadi group showed Musallam shot repeatedly by a teenage boy, after which a second jihadi vowed that IS would “liberate Jerusalem from you filth, by Allah’s permission.”

Lee Gancman contributed to this report.