An ultranationalist group leader who topped Israel's list of most-wanted Jewish extremists has been arrested after a Palestinian baby died in a firebombing in the West Bank.

Meir Ettinger's arrest Monday after being suspected of "nationalist crimes" follows Israel's recent pledge to get tougher on Jewish terrorism.

Domestic intelligence agency Shin Bet, which placed Ettinger at the top of its most-wanted list of Jewish extremists, confirmed it was interrogating him.

Ettinger was arrested in Safed, in northern Israel, "because of his activities in a Jewish extremist organization," a Shin Bet spokesman said. The spokesman would not, however, say if Ettinger is suspected of involvement in Friday's firebombing.

He is accused of being behind a June 18 arson attack on a shrine in northern Israel, where Christians believe Jesus performed the miracle of loaves and fishes.

Administrative detention possible

Ettinger, who is due to appear in court on Tuesday, could face a year of "administrative detention" under the government's harder line against "Jewish terrorists."

Israel usually applies the measure, which dates back to British-mandated Palestine, against Palestinians, allowing renewable six-month periods of detention without trial.

But it can now be used with Jewish detainees in cases of insufficient evidence to go to trial or if the suspect refuses to testify.

Ettinger's grandfather Meir Kahane was a rabbi who founded the racist anti-Arab movement Kach, before he was assassinated in 1990 in New York.

Israel's president threatened after condemning 'Jewish terrorism'

In a separate investigation, police are looking into online threats against President Reuven Rivlin following his condemnation of "Jewish terrorism" after the West Bank firebombing, a presidential spokesman said Monday.

Rivlin had written a Facebook post following the arson attack by suspected Jewish extremists on a Palestinian family's home in the West Bank village of Duma.

The attack killed 18-month-old Ali Saad Dawabsha and critically injured his parents and 4-year-old brother.

"More than shame, I feel pain," Rivlin wrote in both Arabic and Hebrew. "The pain over the murder of a little baby. The pain over my people choosing the path of terrorism and losing their humanity.

"Their path is not the path of the State of Israel and is not the path of the Jewish people. Unfortunately, it seems that so far we've dealt with the phenomenon of Jewish terrorism limply," he wrote, calling for concrete measures against extremists.

Rivlin's post prompted more than 2,000 comments, some positive but others attacking him and recalling Israelis killed by Palestinians.

Police said they had received material from the president's security team and had ordered an investigation to "examine offensive publications against the president on social media."

mh/sms (AFP, AP, dpa)