Israel has said that an Arab citizen used a paraglider to fly illegally into neighbouring Syria, where he planned to join the so-called Islamic State in the four-year-old rebellion against President Bashar al-Assad.
The man's flight across the fortified Golan Heights frontier yesterday jarred Israel, which has seen dozens of its minority Muslim Arabs or Palestinians from East Jerusalem reach the Syrian civil war through legal destinations such as Turkey.
The Israeli military, whose aircraft dropped illumination flares around the Golan overnight before calling off the searches, today issued brief statements describing the paraglider as an Arab from the predominantly Muslim town of Jaljulia.
He was not named. Israeli media gave his age as 23.
Prime Minister Benjamin Netanyahu said the man's citizenship would be revoked as part of a wider policy against militants.
A minister from Mr Netanyahu's rightist Likud party, Ofir Akunis, told reporters that the Israeli Arab had "crossed to the border into Syria ... to join ISIS (Islamic State) forces".
A Syrian rebel whose group operates in the area said the paraglider had come down either in Quneitra province or western Deraa.
Local rebel groups include the Southern Front alliance affiliated with the Free Syrian Army, the al Qaeda-linked Nusra Front, and a group called the Yarmouk Martyrs Brigade, which other rebels believe is affiliated with Islamic State.
Israel is publicly neutral on the Syrian civil war, worried that Assad, a long-time foe with whom it had maintained a stable stand-off, could be toppled by more openly hostile Islamists.
It has outlawed travel there by Israelis on security grounds, and has cracked down on those suspected of trying to breach the ban.
Arabs, most of them Muslims, make up 20% of Israel's population.
Inter-ethnic ties have been strained by this month's surge in Palestinian street attacks and Israeli security clampdowns that has killed more than 52 Palestinians and nine Israelis.
Two videos purportedly by Islamic State and circulated on social media last week called for an escalation in the Palestinian violence, which has been fuelled in part by Muslim anger at stepped-up visits by Jews to a contested Jerusalem holy site.
In one of the videos, a masked gunman speaking Hebrew with an Arabic accent threatens Israelis with all-out religious war.
Israel's Shin Bet security service said it could not authenticate the video but one of its official told Reuters that, with more than 40 Israeli Arabs and East Jerusalem Palestinians having left to join Islamic State in Syria or Iraq,the speaker in the video "could be one of them".