A right-wing Jewish activist has been arrested after a Palestinian baby died in a West Bank firebombing, as police investigated online threats against Israel's president for condemning "Jewish terrorism".

The domestic intelligence service named the activist as Meir Ettinger, a grandson of Meir Kahane, a rabbi who founded the anti-Arab movement Kach and was assassinated in 1990 in New York.

Ettinger was arrested in Safed in northern Israel "because of his activities in a Jewish extremist organization", a Shin Bet spokesman told the AFP news agency.

Police said Ettinger, who is aged around 20, was suspected of "nationalist crimes" but did not accuse him of direct involvement in Friday's firebombing.

Israeli media alleged that he was implicated in a June 18 arson attack on a shrine in northern Israel where Christians believe Jesus performed the miracle of the loaves and fishes.

Ettinger was due to appear in court on Tuesday for a custodial hearing, police said.

Media reports said Ettinger could face a year of "administrative detention" under the government's harder line against "Jewish terrorists".

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

However, Israel's security cabinet recently approved new measures allowing "administrative detention" against Israelis who attack Palestinians, a plan which critics say is ineffective unless the issue of settlements is resolved.

Prime Minister Benjamin Netanyahu's declaration of "zero tolerance" against "fanaticism" on Sunday followed the burning of the Palestinian baby in the occupied West Bank and a deadly stabbing during a gay pride march in Jerusalem.

At his weekly government meeting, Netanyahu said Israel was united against "the criminals among our people".

Commenting on the announcement, Haaretz journalist Gideon Levy dismissed Netanyahu's reaction as "too little, too late" and "not much more than hyprocrisy".

"There is a very clear context of growing violence, nationalism, racism in Israel mainly among the settlers, mainly among nationalist camps," Levy told Al Jazeera.

"As long as this long and brutal occupation is going on, this is inevitable, and it will just get worse and worse."

Over the weekend, thousands of Israelis took to the streets to protest against the attacks and warn against a radicalized and violent fringe that is growing from within the country's religious community.

PHOTO CAPTION

Thousands of Israelis and Palestinians protested against hate crimes over the weekend.

Aljazeera