The First Minister has set out alternative options on income tax which would see "modest" rate rises for higher earners.

Nicola Sturgeon said the time was right to consider increases to protect public services, as she launched a paper on taxation ahead of next month's draft budget.

She indicated that those earning more than £31,000 could face rises next year, although she stressed that the options laid out in the document were "not at this stage firm policy proposals".

The Scottish Conservatives said raising tax would threaten economic growth, while Scottish Labour said none of the government's options would raise enough to end austerity and fund public sector pay rises.

The government's four alternative approaches include having anything up to six tax bands, with three of the four featuring a 50p additional rate and incremental changes to the basic and higher rates.

The approaches could raise between £80 million and £290 million in additional revenue.

Ms Sturgeon said that, when expected increases to the personal allowance are taken into account, none of the approaches would see anyone earning up to £31,000 pay more tax than at present.

"In all four approaches more than 70% of all adults would continue to pay no tax at all or no more tax than they do today," she added.

She said the paper would inform a discussion between all parties ahead of budget negotiations, with compromises needed by all sides.

"Nothing is a foregone conclusion until the Budget is not just presented but passed, but I think you can get the sense from this paper today, what I have said previously and what I am saying today, that I think the time is right to consider modest additional contributions to protect the things we hold dear," she said.

The SNP had previously pledged to keep the basic rate at 20p, and rejected raising the additional rate to 50p in Scotland alone.

The Tories have argued against raising tax in Scotland beyond the rates paid elsewhere in the UK.

Scottish Labour proposed increasing the basic rate and higher rate tax rate by 1p, and an increase in the additional rate to 50p, while the Liberal Democrats want to add 1p to the basic, additional and higher rates.

The Greens proposed a four-band system which would see those on low incomes pay less and those on higher incomes taxed more.

Tory finance spokesman Murdo Fraser said: "None of the tax raising plans they've announced today will increase public spending by a huge amount - but they will all add to the growing perception that Scotland is a high tax country.

"Just as she did with her ill-judged plans for a second referendum, Nicola Sturgeon has rushed ahead with this plan without taking account of the evidence or the facts.

"The Scottish Conservatives will take a measured approach on tax, with sustainable economic growth at its heart."

Finance spokeswoman Jackie Baillie said: ''To end austerity you need to raise more than £800 million in revenue over the next two years, that's before we consider additional commitments.

''Yet the Government's proposals published today in the tax paper raises a maximum of £290 million - that doesn't even come closing the gap, there is a black hole in the budget and more services would end up being cut."

Greens co-convener Mr Harvie said: "Greens have been pushing hard to make use of Scotland's new income tax powers and it's hugely significant that the Scottish Government is now looking at options which are more creative than simply tinkering with the basic rate as some parties have suggested."

Lib Dem leader Willie Rennie said: "We welcome the willingness of the SNP to have a debate. It is significant that the SNP are prepared to move and change their policy."