Labour leadership contender Jeremy Corbyn has suggested that Tony Blair could be made to stand trial for war crimes over the invasion of Iraq.
The veteran left winger said the 2003 conflict was an "illegal war" and that the individuals who "made the decisions that went with it" should face justice.
His comments, in an interview with BBC2's Newsnight, will further fuel the tensions in an increasingly heated leadership contest.
Mr Corbyn, a long-standing critic of Mr Blair, said that with the Chilcot inquiry report coming, the former prime minister was reaching the point when he was going to have to deal with the consequences of his actions.
"We went into a war that was catastrophic, that was illegal, that cost us a lot of money, that lost a lot of lives, and the consequences are still played out with migrant deaths in the Mediterranean, refugees all over the region," he said.
Asked if Mr Blair should be charged with war crimes, he said: "If he's committed a war crime, yes. Everyone who's committed a war crime should be.
"I think it was an illegal war, I'm confident about that, indeed (former UN secretary general) Kofi Annan confirmed it was an illegal war, and therefore he has to explain to that.
"Is he going to be tried for it, I don't know. Could he be tried for it? Possibly."
Pressed on whether he would like to see Mr Blair put on trial, he said: "I want to see all those that committed war crimes tried for it, and those that made the decisions that went with it."
His remarks are likely to infuriate Mr Blair's supporters in the party while once again highlighting the deep divisions that remain over the most controversial decision of his premiership.
They come after the former prime minister angered many on the left with his suggestion that anyone in the party whose heart told them they should vote for Mr Corbyn should "get a transplant".
Meanwhile Andy Burnham is to pledge a "line-by-line" re-nationalisation of the railways if he succeeds in his bid for the Labour leadership.
The shadow health secretary will set out his plans for a "progressive" programme to take the railways back into public ownership when he publishes his campaign manifesto on Thursday.
He will also commit to the establishment of a new "national rail" government body, answerable to the transport secretary, to ensure passengers are always offered the cheapest ticket for their journey, and the re-regulation of the bus services.
His announcement, disclosed in the Daily Mirror, is likely to be seen as an attempt to claw back ground from Mr Corbyn whose gathering campaign momentum has alarmed the shadow cabinet.
"We need a new approach to our railways, one that puts passengers before profit. That's why I will work to bring the railways back under public control and public ownership," his manifesto will say.
"Under my leadership, Labour will ensure there is proper and accountable public control of the railways, with passengers' interests put first - an end to the fragmentation and privatisation."