State prosecutors have appealed to Israel’s High Court in the case of an Arab resident of Nazareth, Maharan Haldi, 20, who was arrested and convicted after he went to Syria and Iraq to fight with the Islamic State and then returned to Israel, Israel Radio reported on Wednesday. A lower court sentenced Mr. Haldi to three and a half years in prison, which prosecutors consider too lenient. Israel radio said the court in Nazareth had taken into account Mr. Haldi’s regret and his personal background.

Palestinian citizens of Israel, about a fifth of the country’s population, have rarely participated in organized armed attacks. Those who have gravitated toward the Islamic State are a tiny minority. Experts and commentators said some might be attracted because of longstanding grievances about discrimination in Israel.

“Youths are looking for an outlet,” said Salim Shehada, a veteran reporter at Ashams, a local Arabic radio station. He added that Muslim families in Israel were growing concerned that Islamic State recruiting could seduce their children.

“The unemployment, the spreading crime inside Arab villages in Israel, the dark future that many of these youths face is leading to a certain kind of extremism and support for these ideas,” Mr. Shehada said.

Daniel Nisman of the Levantine Group, a geopolitical risk analysis company based in Tel Aviv, said the most recent arrests suggested the first plot to carry out an Islamic State-inspired attack in Israel.

“I think, like in many places, it is gradually heading toward people who will try to do something like that in the name of the Islamic State, similar to the attack in San Bernardino,” Mr. Nisman said, referring to the massacre in California last week. He described the suspects as “wannabes who have access to guns.”

Shin Bet said in a statement that it had obtained information that the suspects who were recently charged had been “holding suspicious meetings and conducting weapons training.” It did not explain how the agency had received the information. But it said that it had become apparent from the interrogation that the suspects had grown more religiously observant over the last year and, during their meetings, “expressed support for the Islamic State and praised jihad against non-Muslims.”