A Canadian-Israeli who was the first foreign woman to help Syria's Kurds fight Islamic State has left the front lines and returned to Israel, citing the spread of Iranian influence in the war zones among her reasons.

After eight months in which she was often incommunicado, stirring rumours that she had been taken captive, Israeli media feted Gill Rosenberg's sudden return on Sunday. But she may still face a legal reckoning for her unauthorised travels.

The 31-year-old former Israeli army volunteer said the lessons of the Holocaust drove her to help protect the Kurds and other Middle East minorities menaced by Islamic State advances.

"I think we as Jews, we say 'never again' for the Shoah, and I take it to mean not just for Jewish people, but for anyone, for any human being, especially a helpless woman or child in Syria or Iraq," Rosenberg told Israel's Army Radio on Monday.

"But in the past few weeks I think a lot of the dynamics have changed there, in terms of what's going on in the war. The Iranian involvement is a lot more pronounced. Things changed enough that I felt that it was time to come home."

Rosenberg started out with Kurdish YPG guerrillas in Syria before moving to the Dwekh Nawsha, a Christian militia in Iraq. Both countries are formally at war with Israel, which bars its citizens from traveling there. Iran is among regional powers sending forces to battle Islamic State in Iraq.

The Israeli internal security agency Shin Bet said it questioned Rosenberg after she landed in Tel Aviv. It did not elaborate on whether she would face criminal charges, but an Israeli justice official told Reuters it appeared unlikely.

Rosenberg's native Canada, from which she emigrated alone to Israel, had also urged her to get out of Syria. The Canadian embassy in Israel did not immediately comment on her return.

US authorities could pose more of a challenge, however.

In 2009, Rosenberg was arrested in Israel over an international phone scam and extradited to the United States, where she served time in prison. Yahel Ben-Oved, one of her lawyers, said Rosenberg won early release in 2013 on condition that she remain paroled either on US or Israeli soil.

"I believe she may have violated this by going to Syria," Ben-Oved told Reuters. "This could be a problem for her."

US officials said they were looking into the case.

Rosenberg declined a Reuters request for an interview, saying she would speak to foreign media later in the week.

Reuters sources familiar with the YPG and Dwekh Nawsha confirmed that Rosenberg had served with both.

"We were, like, under 2 km (1 mile) from Daesh (Islamic State) the whole time, for the most part," Rosenberg told Army Radio. "There were some pretty major firefights, but, you know, a lot of it was just holding lines."

She said she was ordered to keep quiet about her Israeli citizenship while with the YPG, a militia with a historically pro-Palestinian leaning.

"The Kurds love Israel. They love Israel and they love the Jewish people. But among the ranks of the YPG there's also local Arabs and other people that might not be such big fans of Israel," she said.