Chancellor George Osborne and Treasury Secretary Danny Alexander have insisted it is "wrong" to suggest there would be a currency union between the UK and an independent Scotland.
A Guardian report quotes an unnamed minister who says a deal could be done to allow Scotland to use the pound even if it votes to leave the UK.
But Mr Osborne and Mr Alexander said "there will not be a currency union".
Scotland's deputy first minister Nicola Sturgeon welcomed the Guardian story.
Continue reading the main storyAs for the unnamed minister, better stay unnamed. Otherwise, there will be a queue of ministerial colleagues waiting to shake you warmly by the throat.”End Quote The Guardian quotes a UK government minister who it says would play a central role in the negotiations over the break-up of the UK if there were a yes vote.
It quotes the unnamed minister as saying: "There would be a highly-complex set of negotiations after a yes vote with many moving pieces.
"The UK wants to keep Trident nuclear weapons at Faslane and the Scottish government wants a currency union - you can see the outlines of a deal."
The Treasury, along with Shadow Chancellor Ed Balls, has previously ruled out a currency union.
In a joint statement, George Osborne and Danny Alexander said: "There will not be a currency union in the event of independence. The only way to keep the UK pound is to stay in the UK. Walking out of the UK means walking out of the UK pound.
"A currency union will not work because it would not be in Scotland's interests and would not be in the UK's interests.
"Scotland would have no control over mortgage rates, and would be binding its hands on tax and funding for vital public services."
The statement added: "The Scottish government are proposing to divorce the rest of the UK but want to keep the joint bank account and credit card.
Continue reading the main storyThe UK would not put its taxpayers at risk of bailing out a foreign country and its banks. Parliament wouldn't pass it, and the people wouldn't accept it”End Quote George Osborne and Danny Alexander UK government ministers Continue reading the main story
This was supposed to be the No campaign's trump card, but as the polls show it has backfired badly”End Quote Nicola Sturgeon Scotland's Deputy First Minister "The UK would not put its taxpayers at risk of bailing out a foreign country and its banks. Parliament wouldn't pass it, and the people wouldn't accept it.
"Any suggestion to the contrary is wrong."
Scottish Secretary Alistair Carmichael said: "An anonymous, off-the-record quote does not change the stark reality on the currency."
Nicholas Watt, the Guardian journalist who wrote the story, spoke to BBC Radio Scotland's Good Morning Scotland programme.
He said: "Their [UK government's] absolute trump card in this campaign is to say there will be no currency union and they will be saying that from now until midnight on the 17th September.
"But in the unlikely event of a Yes vote, in a very lengthy negotiation, you may well find that a trump card in a campaign will come quite different in these negotiations."
Last month, the Chancellor said a vote for Scottish independence would mean walking away from the pound.
Scottish First Minister Alex Salmond accused him of "bluff and bluster".
The Scottish government, led by Mr Salmond's SNP, has argued that keeping the pound and the services of the Bank of England as part of a currency union under independence made sense for both Scotland and the rest of the UK.
But Mr Osborne's declaration that there would not be a currency union was followed by Mr Alexander and Labour's Ed Balls insisting that they would not agree to share sterling if Scotland voted for independence in September.
Danny Alexander and George Osborne issued a statement saying there would be no currency union 
Scotland's currency after independence has become a major issue in the campaign 
Deputy First Minister Nicola Sturgeon said the UK government's approach was backfiring Scotland's Deputy First Minister Nicola Sturgeon said: "This was supposed to be the No campaign's trump card, but as the polls show it has backfired badly - the gap between Yes and No has halved since November, and most Scots simply do not believe the bluff and bluster we had from George Osborne, Ed Balls and Danny Alexander."
Continue reading the main storyWho? Voters in Scotland will go to the polls to vote on their country's future.
What? They will be asked the yes/no question: "Should Scotland be an independent country?"
When? The vote takes place on Thursday, 18 September, 2014.
She added: "The reality is that a currency union is every bit as much in the interests of the rest of the UK as an independent Scotland, and that is why Westminster will agree to one."Scotland is the rest of the UK's second biggest trading partner, and not sharing sterling would cost businesses south of the border an extra £500m in transaction costs."
Voters in Scotland will be asked the yes/no question: "Should Scotland be an independent country?" when the independence referendum is held on 18 September.