Jeremy Corbyn has refused to apologise for being present when a wreath was laid in memory of some of those accused of the 1972 Munich terror attack.
The Labour leader has been criticised over the 2014 event in Tunis, with Israel's PM Benjamin Netanyahu saying he deserved "unequivocal condemnation".
Mr Corbyn said he had attended to take part in a ceremony honouring innocent victims of a 1985 Israeli air strike.
And he condemned the Munich attack, describing it as "appalling".
Mr Corbyn has faced fresh questions about the 2014 conference after the Daily Mail said he was pictured with a wreath near memorials to members of the Black September organisation. The Palestinian group killed 11 hostages from the Israeli Olympic team and a West German police officer during the 1972 summer games.
Asked about calls for an apology, he said: "I'm not apologising for being there at all."
He said he had been present in Tunis at a conference "to try and promote peace in the Middle East".
In a reference to the 1985 bombing of the Palestine Liberation Organisation headquarters in the Tunisian capital, he added: "I remembered those that had died in an attack on Tunis by the Israeli air force which was condemned by the whole world."
He had "witnessed many other people laying many wreaths", he said, but his had been for victims of the 1985 bombing.
"There are other people in that cemetery, as are indeed in many other cemeteries around the world, but a wreath was laid in memory of those that died," he said.
The Labour leader said he had attended the conference alongside people from other political parties and representatives from around the world.
One of these was Tory peer Lord Sheikh, the founder of the Conservative Muslim Forum, who told the Press Association: "If there was a wreath-laying ceremony I was not aware of the wreath-laying ceremony. I did not go to the ceremony."
Labour MP Luciana Berger had taken issue with the Labour leader's response on Monday when asked whether another wreath had been laid, and whether it honoured terrorists. Mr Corbyn had simply replied that a wreath "was indeed laid", adding: "I was present when it was laid. I don't think I was actually involved in it."
Ms Berger tweeted: "Being 'present' is the same as being involved.
"When I attend a memorial, my presence alone, whether I lay a wreath or not, demonstrates my association and support. There can also never be a 'fitting memorial' for terrorists. Where is the apology?"