(Reuters) - A furor over alleged anti-semitism in Britain’s main opposition party widened on Monday when Israeli Prime Minister Benjamin Netanyahu and Labour Party leader Jeremy Corbyn exchanged accusations on Twitter over Israeli-Palestinian bloodshed.

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Labour has been wrestling accusations of anti-semitism for months, and Corbyn has previously apologized for what he has described as “pockets” of anti-semitism in the organization.

Britain’s right-leaning Daily Mail on Friday reported that Corbyn, on a visit to Tunisia in 2014, had laid a wreath at the graves of members of a Palestinian group that killed 11 Israeli athletes and a German policeman at the 1972 Munich Olympics.

It said the cemetery houses a memorial to the dozens killed in the 1985 Israeli bombing of the Palestine Liberation Organisation headquarters in exile in Tunis, as well as the graves of members of Black September, a PLO splinter group that carried out the Munich attack.

It published a photograph it said showed Corbyn standing near the graves of Black September members.

Labour said Corbyn, a staunch supporter of the Palestinian cause, was in Tunis to honor the victims of the 1985 raid.

Unimpressed, Netanyahu said in a tweet:

“The laying of a wreath by Jeremy Corbyn on the graves of the terrorists who perpetrated the Munich massacre and his comparison of Israel to the Nazis deserves unequivocal condemnation from everyone – left, right and everything in between.”

Corbyn responded: “Netanyahu’s claims about my actions and words are false. What deserves unequivocal condemnation is the killing of over 160 Palestinian protesters in Gaza by Israeli forces since March, including dozens of children.”

The Labour Party said Corbyn did not lay a wreath at the graves of anyone linked to Black September and he condemned the Munich attack. Corbyn however told reporters on Monday: “I was present when (a wreath) was laid, I don’t think I was involved in it,” adding that the visit was a peace-seeking exercise.

Despite deep divisions in the Conservative government as it negotiates Britain’s exit from the European Union, Labour’s poll standing appears to have been damaged by the anti-semitism row.

A YouGov poll last week showed that 39 percent of those asked would vote for the Conservatives, a gain of one point for May’s party compared to last week when the two biggest parties were level. Labour dropped three points to 35 percent.