Jeremy Corbyn has said he will “open discussions” with the Scottish government over an independence referendum if he wins the election.
But the Labour leader said he would “ask them to think very carefully about it”.
He also insisted he would not do a deal with the SNP to gain power at Westminster.
The Conservatives claimed Mr Corbyn and the SNP were already working on a potential post-election arrangement.
The Labour manifesto commits the party to opposing a referendum, which it describes as “unwanted and unnecessary” – with Mr Corbyn predicting independence would lead to “turbo-charged austerity”.
And Scottish Labour’s manifesto states that it will “never” support independence – with leader Kezia Dugdale giving a “cast-iron guarantee” that her party will oppose a second referendum.
But earlier this year, Mr Corbyn said he would be “absolutely fine” with a referendum being held if the Scottish Parliament voted for one.
SNP leader Nicola Sturgeon, who is Scotland’s first minister, wants a referendum in the autumn of next year or the spring of 2019, with the Scottish Parliament formally backing her call in March.
However, she would need the consent of the UK government for a legally-binding vote to be held – and Prime Minister Theresa May has repeatedly said that “now is not the time”.
On Monday, Mr Corbyn was asked in an interview with Bauer and Global radio stations what he would say to Ms Sturgeon if he was to become prime minister after the election on 8 June.
‘Listen very carefully’
He replied: “I’ll obviously open discussions with the government in Scotland and listen very carefully to what the Scottish Parliament says.
“I would ask them to think very carefully about it and suggest it would be much better to have this question dealt with at the conclusion of what are very serious and very important Brexit negotiations.
“I am utterly determined to achieve tariff free trade access to the European markets to protect manufacturing and service jobs all across the UK, all across Scotland, Wales and England as well of course.”
A spokesman for Mr Corbyn later insisted: “Jeremy Corbyn and Scottish Labour have repeatedly said that a second independence referendum is both unwanted and unnecessary. Labour firmly opposes a second independence referendum”.
In a BBC interview at the weekend, Ms Sturgeon said she would try to form an alliance to pursue “progressive policies” and keep the Conservatives out of government if the general election results in a hung parliament.
But she also predicted that the Conservatives would win another majority – and said Mr Corbyn was not credible as a potential prime minister.
Responding to her comments, Mr Corbyn said: “There will be no deals. There will be no alliance. We’re fighting this election to win.
“Only Labour or the Tories can win this election and voting Labour is the only way to remove Theresa May from office and build a Scotland for the many not the few.”
Meanwhile, Mrs May warned Conservative activists that the party has only to lose six seats for its Commons majority to disappear, opening the way to Downing Street for Labour.
The prime minister said: “That could mean in just 10 days’ time a government in chaos, Jeremy Corbyn in No 10, John McDonnell in the Treasury, Diane Abbott in the Home Office and Nicola Sturgeon and the Lib Dems pulling the strings.”
She added: “I’ve been clear talking about a second independence referendum in Scotland at this time.
“Now is not the time because what we need to be doing now as we face this historical moment as we need to get the Brexit negotiations right, what we need to do is to be working together and not pulling apart.
“I believe Nicola Sturgeon said yesterday that she didn’t think Jeremy Corbyn was capable of being prime minister but at the same time also said that she would prop him up and push him into government.”
Scottish Liberal Democrat MSP, Alex Cole-Hamilton said: “Much like Jeremy Corbyn’s position on Brexit his position on independence has become confused and chaotic. Every time Jeremy Corbyn speaks somebody has to follow and clean up the mess.
“Scottish Labour must be pulling their hair out as last time I checked this wasn’t their policy.
“Liberal Democrats are clear, every MP elected on the 8 June is a MP that will stand against the SNP’s plan for another divisive independence referendum.”