Ed Miliband has condemned the social media abuse directed at Luciana Berger.
The Labour leader said the "shocking attacks" on Ms Berger and fellow Jewish Labour MP Louise Ellman had "highlighted the new channels by which antisemites spread their vile views".
He called on social media sites to do "all they can" to protect users from online abuse.
In wide-ranging comments posted on Facebook this week, he said the growth of antisemitism in Britain should serve as a wake-up call to those who think Jew-hatred is a thing of the past, he believed. Mr Miliband said he had spoken to Jewish families who expressed concern for their futures in Britain and urged a zero tolerance approach to tackle the problem of antisemitism.
He also said it was essential to use "calm and responsible language" when discussing Israel, especially when criticising the actions of the Israeli government.
Sites must do all they can to protect users
The Labour leader referred to Community Security Trust figures which show more than 300 antisemitic incidents took place in July - a 400 per cent increase on the same month in 2013.
"There have been violent assaults, the desecration and damage of Jewish property, antisemitic graffiti, hate-mail and online abuse," he wrote.
"But the recent spate of incidents should serve as a wake-up call for anyone who thought the scourge of antisemitism had been defeated and that the idea of Jewish families fearful of living here in Britain was unthinkable.
"Some have told me how, for the first time in their lifetime, they are scared for their children's future in our country. Others have expressed a general unease that this rise in antisemitism could signal that something has changed - or is changing - in Britain.
"I take these concerns very seriously because it is the responsibility of all to ensure that Britain's traditions of respect and tolerance are upheld.
"We need a zero-tolerance approach to antisemitism in the UK and to reaffirm our revulsion to it in all its forms."
Mr Miliband said Labour would continue to fight intolerance and said he would never excuse attacks on British Jews which followed conflicts in the Middle East. That approach would form part of a Labour government's foreign policy, he suggested.
But the Campaign Against Antisemitism said Mr Miliband's comments were nothing more than "vague posturing".
The grassroots anti-hate group said: "Calling for zero tolerance on Facebook without offering specifics, months too late, while making a pointless link to British policy on Israel - a topic on which Labour MPs regularly make extremely inflammatory comments with impunity - is vague posturing at a time when we need urgent action and real leadership."
