Scottish Labour leader Kezia Dugdale has sought to clarify reports she might back Scottish independence if it could secure Scotland's EU membership.
In an interview with the Fabian Review she was quoted as saying it was "not inconceivable" in such circumstances.
But she later insisted she would vote to stay in the UK in any future referendum and opposed one being held.
The Scottish Conservatves claimed Labour could not be trusted to defend the Union.
In the interview Ms Dugdale also spoke for the first time about her private life, telling Mary Riddell, "I have a female partner. I don't talk about it very much because I don't feel I need to."
Ms Dugdale was asked where her "loyalty" would be if there was an overall vote to leave in the EU referendum but the majority of Scots wanted to remain.
She replied: "I've never contemplated that. I really wouldn't like to choose, because what I want to do is the best possible thing for Scotland. (I would be) putting Scotland first."
When pushed on the topic and asked if she would "argue, for Scotland's sake, against the UK Union?", the Scottish Labour leader was quoted as saying: "Possibly. It's not inconceivable."
But she later clarified her position, pointing out that in the leaders' debate earlier this week ahead of the Scottish Parliament election, she had ruled out a second independence referendum.
She said: "We won't introduce one in government and we would vote against one if it's introduced by any other party.
"Our manifesto will make that commitment clear, unlike the Tories who have said they would support a second referendum if the SNP are elected on a manifesto promising one.
"I campaigned as hard as anybody to ensure that Scotland remained part of the UK.
"The collapse in the oil price showed that the best way to secure our public services is to stay in the UK. I would vote to stay in the UK in any future referendum.
"After the collapse of the economic arguments for independence, the biggest threat to the Union is now the Tory party civil war on Europe.
"Both Brexit and leaving the UK would be bad for Scotland. If we leave the EU because of Tory infighting Nicola Sturgeon will do everything she can to use that as an excuse for another independence vote.
"I want to stay in both unions and will vote to stay in both."
The Scottish Conservatives said the Fabian Review interview showed Labour could not be "trusted to defend the decision of two million Scots to stay part of the UK".
A Tory spokesman added: ""The idea that Scotland's place in the United Kingdom is in some way dependent on Britain's membership of the EU is offensive.
"Scotland helped build the UK and is an integral part of it - confirmed by the referendum vote just 18 months ago.
"With the SNP about to prepare a fresh drive for independence, we need to stand up for our place in the UK. It now appears Labour are simply incapable of doing that."
Asked in the Fabian Review interview about her private life, Ms Dugdale said: "I have a female partner. I don't talk about it very much because I don't feel I need to.
"And there's something too about how meteoric my career has been. I am generally calm, almost serene. I don't get easily stressed or battered.
"But I need a bit of stability to do that, and that means my private life is my private life. That's the thing I just have to have that nobody gets to touch, and that gives me the strength to be calm elsewhere."
Ms Dugdale also spoke of her respect for SNP leader Nicola Sturgeon, despite their political differences.
She said: "Women owe it to other women to say: 'Look at that. Isn't it fabulous?'
"It would be completely ridiculous if I wasn't to recognise how talented she is.
"When I was a Labour researcher and she was health minister, we did cross paths more regularly, in the canteen. She was very, very kind to me then and encouraged me a lot."