The Shin Bet said the two brothers from Umm al-Fahm in central Israel, charged in a Haifa court, had been arrested.
The Shin Bet said the two brothers from Umm al-Fahm in central Israel, charged in a Haifa court, had been arrested in July on suspicion of support for IS.
One of them, Mahmud Abdel Karim Kassem Jabarin, 25, had been in contact with an IS member in Syria and former resident of Umm al-Fahm, according to the Shin Bet, which alleged he had also sworn allegiance to the jihadist group.
An automatic weapon had been discovered in a sweep of the brothers' home.
On July 14, three Arab Israelis from Umm al-Fahm shot and fatally wounded two policemen near the ultra-sensitive Al-Aqsa mosque compound in Israeli-annexed east Jerusalem, before they were gunned down.
The attack triggered a two-week-long crisis as Israel temporarily installed metal detectors and security cameras at the site.
The Shin Bet said IS sympathisers among the Jewish state's Arab minority now posed a "serious security threat" for Israel.
By the end of 2016, 83 people, most of them Arab Israelis, were behind bars in Israel as suspected IS sympathisers, up from just 12 a year earlier, according to the Haaretz newspaper.
Some of them were arrested for planning to travel to Syria or Iraq to fight alongside the jihadists, or on their return to Israel, others for contacts on the internet with IS militants abroad or for planning attacks.
The Shin Bet estimates 50 Arab Israelis are currently fighting in IS ranks in Syria and Iraq.