Tony Blair has accused Jeremy Corbyn's Labour of doing a "terrible thing" by alienating the Jewish community.
The former PM said Labour's antisemitism crisis was a "truly shameful episode" for the party, in an interview with Euronews.
And he appeared to blame Mr Corbyn's "statements" for contributing to the problem and said there was "an element to his leadership" that was at odds with the party's anti-racist principles.
When asked whether he thought Mr Corbyn was an antisemite, Mr Blair said: "In a sort of classic sense, I don't think he is.
"But his statements and the way the party have handled this... It really doesn't matter if I call him that or not."
He continued: "This has been a truly shameful episode for Labour and it's causing real difficulties for those of us who stay in (the party) and want to see it come back to sense; to see a situation in which the Jewish community in this country feel really alienated and worried and anxious... that's a terrible thing to have done."
Mr Blair's intervention comes just after his successor as PM Gordon Brown gave a barnstorming speech at the Jewish Labour Movement conference, where he received a standing ovation for an address that called on the party to adopt the internationally recognised IHRA definition of antisemitism.
The party's refusal to do this, and to opt instead for a watered-down version, has fuelled an intense row between the party and its Jewish supporters.
Jewish MP Luciana Berger described it in an interview with the JC as a "sickening summer of antisemitism".
On Tuesday, the party's governing body, the NEC, will vote on whether to adopt the IHRA definition.
Mr Blair told Euronews antisemitism was part of "a deeper problem with the politics of Jeremy Corbyn and the people round him" because of their "visceral anti-Western position" and their hostility to Israel.
"If you look at where they make their attacks, where they don't make their attacks: they will attack people who support the West and they will basically defend people who are anti-West," he said.
"In a way, their attitudes to Israel got kind of caught up in that bigger and broader argument."
Mr Blair was asked whether he thought Labour was now racist, to which he said: "The party that I know and that I grew up in is definitely not a racist party."
But he added there was an "element to this leadership" that was "very difficult to reconcile with the proper principles of the Labour Party".