Claims that Scotland will be forced to cut funding to the National Health Service (NHS) to plug a black hole in finances are "absolutely untrue", the First Minister has insisted.

The NHS is facing a funding gap of up to £450 million and major changes will be needed to find savings, private documents passed to the BBC suggest.

According to the papers, which were presented to a meeting of health board chief executives and civil servants last month, new obligations are "not fully funded" and the "status quo in terms of service and workforce planning is not an option".

Better Together leader Alistair Darling told BBC Radio Scotland that the First and Deputy First Ministers had been deceiving voters over the future of the NHS.

He told Good Morning Scotland: "Today we learn that Alex Salmond and Nicola Sturgeon have been deceiving us.

"We find that they are planning to cut £450 million from Scotland's health budget, something over which they have total control, and yet they were going to keep this under wraps until after the referendum.

"I find that quite appalling after all the things they have been saying about the health service, all these scare stories and all the time they have known that these cuts were coming along but we weren't going to be told about it until after the polls close."

The funding gap is put at between £400 million and £450 million during the 2015/16 financial year, according to the papers - a level described as "significantly in excess of that previously required".

Options that health boards will have to consider include centralising hospitals and closing services, the papers say.

The documents state: "The status quo and preservation of existing models of care are no longer an option given the pressing challenges we face."

Mr Salmond said cuts claims were "mythical" and pointed to plans passed in the Scottish Parliament earlier this year that the overall budget goes from £11.9 billion to £12.7 billion next year.

He told Good Morning Scotland: "What this paper does is part of the normal planning in the health service.

"It says that we'll need 3.5% efficiencies in order to meet commitments in the rising cost of procedures in the health service.

"In the last six years we have managed 3% and that's all been ploughed back, every single penny of it, into the health service. That's why we have increased funding in real terms."

Scottish Liberal Democrat leader Willie Rennie called on Health Secretary Alex Neil to give "immediate answers" about NHS finances.

He said: "We need immediate answers from the Health Secretary on his £400 million secret NHS cuts plan.

"This would be a devastating cuts agenda which would fundamentally undermine the ability of our NHS. It is unpardonable that this significant news has been kept hidden from voters.

"Despite this meeting taking place in early August, the nationalists proceeded to spread fear about the future of our NHS.

"But they knew all along that the only real risk to our NHS was their independence plans. We need to know who at the top of the nationalist government knew about these plans."