Jeremy Corbyn has said that he got his words wrong when he initially appeared to reject the Brexit backstop.
He said he supported the proposal, but gave the impression in an interview last year that he was against it.
The backstop is the insurance policy to avoid a hard border between NI and the Republic after Brexit, unless and until another solution is found.
“I actually did [support it] but it was a misunderstanding in my use of language.”
The Labour leader added: “What I said was there were concerns about the way in which it could lock you into a customs union from which you could never negotiate any removal.”
Westminster MPs rejected the backstop and withdrawal agreement negotiated by former Prime Minister Theresa May, which would have kept all of the UK in a “temporary customs territory” with the EU and would have seen Northern Ireland also continuing to follow other EU rules.
Unionists in Northern Ireland oppose the backstop, arguing it would create a border down the Irish Sea.
Earlier this year, Mr Corbyn called for changes to the backstop and his MPs voted against Mrs May’s deal.
His comments caused unease among some Labour members.
Questioned on why he used similar language to the Democratic Unionist Party (DUP) when he said there should not be a border down the Irish Sea, he said: “Let me be clear about this. I want to see the Belfast Agreement operational. I do not want to see a hard border.
“I want to see a continuation of trade between Northern Ireland and the Republic.”
The Labour leader denied his party was playing politics with the border issue.
Mr Corbyn said he wanted to make sure there was an arrangement in place that “protects the border.
“Call it the backstop, call it what you like, but make sure it protects the principle of the open border,” he said.
In a wide-ranging interview in advance of the Labour Party conference, Mr Corbyn also spoke about the prospect of a border poll and whether he would see a united Ireland in his lifetime.
“I don’t think it [a border poll] is soon. It is some way off,” he told BBC News NI.
“If there is a demand for a border poll within the terms of the Belfast Agreement and supported by the government in Dublin, I think we would obviously consider it.”
The leader of the opposition said that if a border poll was called, a Labour government would not take a position on Northern Ireland’s future.
He said a united Ireland was a “decision for the people of Ireland”.
The Labour Party conference begins this weekend in Brighton.
You can see the Jeremy Corbyn interview on BBC Newsline at 18:30 BST and on The View on BBC One at 22:35 BST