Jeremy Corbyn criticised Tony Blair for intervening in the EU referendum debate after the former Prime Minister called for pro-Europeans to form a new cross-party movement against Brexit.
The Labour leader urged Mr Blair to "respect the result" of the vote to leave and to put his energy towards building relations in Europe.
Mr Corbyn, who was quizzed on the comments after addressing Labour's local government conference at Warwick University, said: "Well, it's not helpful.
"I would ask those to think about this - the referendum gave a result, gave a very clear decision on this, and we have to respect that decision, that's why we didn't block Article 50.
"But we are going to be part of all this campaigning, all these negotiations about the kind of relationship we have in Europe in the future."
He added: "The referendum happened, let's respect the result. Democracy happened, respect the result."
Mr Blair, speaking at the London headquarters of Bloomberg on Friday, suggested that the Labour Party had aided Brexit and called for a cross-party effort in the absence of an effective opposition.
"The debilitation of the Labour Party is the facilitator of Brexit. I hate to say that, but it is true," Mr Blair said.
"What this means is that we have to build a movement which stretches across party lines; and devise new ways of communication."
But Mr Corbyn said: "I don't quite know what Tony means there.
"Our party membership has more than doubled, we had a big campaign to remain and reform the European Union.
"We are now pursuing a policy which will try and protect jobs and conditions across this country but also maintain a good relationship with colleagues across Europe."
He added: "We are going to be outside the European Union. We are not leaving the continent of Europe, we are still going to work with them.
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"I think it would be helpful if people put their energies in the direction of building those good relations and ensuring we have a viable economy, not some offshore tax haven bargain basement, doing deals with Trump's America."
Mr Corbyn said he would ensure the Labour party respects the results of the referendum.
He said: "My job is to take our party forward into an investment-led economy that reduces inequality in this country, that builds houses when people need them, that gets the good jobs people need in the hi-tech industries the National Investment Bank will fund.
"Get on board with that strategy."
