Jeremy Corbyn has hit back at claims by Tony Blair that he is only interested in "protest" rather than real political power.
In his most critical remarks yet about Corbyn, the former Labour Prime Minister said "Jeremy's the guy with the placard", unable to change people's lives because he was not in Government.
Blair also slammed his successor for deciding to "do nothing" to protect innocent Syrians from President Assad's barrel bombs.
Speaking to Bloomberg Television, the ex-PM said: "There are two types of politicians on the left, and there always have been. There’s a guy whose face is on the placard, right? And that’s me. Hate that guy.
"So you’re the person in power, taking difficult decisions, some people support you, some people don’t support you, but you become a figure of controversy and some people, they go out and they protest against you. That’s my type of politics.
"You’re the face on the placard. Jeremy’s the guy with the placard. He’s the guy holding it. One’s the politics of power, and the other’s the politics of protest. And the two are different. And in the end, if you want to change people’s lives, you’ve got to be for the politics of power."
Corbyn has suggested that if the Chilcot Report finds Blair legally responsible for failures in Iraq, he should be tried for 'war crimes'.
But the former premier suggested that it was Corbyn who was to blame for the deaths of Syrians killed by the regime, after he refused to vote for military action in the country.
“I’m accused of being a war criminal for removing Saddam Hussein -- who by the way was a war criminal -- and yet Jeremy is seen as a progressive icon as we stand by and watch the people of Syria barrel-bombed, beaten and starved into submission and do nothing,” Blair said.
But Corbyn's spokesman rejected the claims, and went further to say that he would never share a platform with the ex-PM.
"If he's suggesting that Jeremy Corbyn is leading a politics of protest, I would say that's not correct," the spokesman said.
"Jeremy Corbyn is leading the Opposition and building support against the Conservative government. What Tony Blair says is a matter for him. We are quite clear about our position in Syria and how you achieve peace."
When asked if there were any plans to appear alongside Blair in the EU referendum, the Labour spokesman said that the former PM had been supporting the Britain Stronger in Europe campaign, which was separate from the Labour In campaign.
"We are not sharing platforms with the Stronger in Europe campaign...There are no plans to share a platform with Tony Blair."
The spokesman added that Corbyn had made clear he would not be taking part in any 'Tory campaigns' on Europe and felt he was more effective in getting out the Labour vote for 'Remain' by connecting with their concerns on issues like workers' rights.
Blair and Corbyn have rarely seen eye-to-eye over the years, even though many Labour MPs feel their current leader fails to recognise the good work that the Blair governments did on domestic policy.
During the Labour leadership race in 2015, Blair suggested that anyone who wanted to vote for Corbyn needed a 'heart transplant' - and faced a backlash from party members.
In his Bloomberg interview, the former PM said that global politics - from Trump and Sanders in the US to Corbyn in the UK - was now about 'rattling the cage'.
But he said it was time for more 'muscularity' from those in the centre-ground.
"I think something has changed and I think you know the center ground has lost its, what I would call its muscularity, its traction on the political debate, I think we have got to get it back.
"What I find both sides of the Atlantic is it’s a sense amongst people that they’re frustrated by the system, they don’t feel the system is responding to their anxieties and concerns and they want almost to, it’s about rattling the cage."
Blair also rejected the idea - promoted by some Labour MPs and supporters of Corbyn - that Sir Philip Green should be stripped of his knighthood for his handling of the BHS affair.
Asked if he agreed with the idea, Blair said: "No, I don’t take it beyond that at all. And you’ve also got to realise that over a long period of time, there have been many, many jobs created in the UK."