Nicola Sturgeon has urged voters to back the SNP for "strong opposition" to the Conservative government ahead of the release of its election manifesto.

The publication of the document, delayed from last week due to the Manchester terror attacks, comes as the SNP leader suggested the possibility of a "progressive alliance" pursuing "progressive policies" at Westminster if the June 8 election resulted in a hung parliament.

Speaking ahead of the launch of the manifesto in Perth, Sturgeon emphasised the likelihood of a Tory victory despite a narrowing in the polls with Labour.

The SNP leader is hoping to build on her party's 2015 success of winning a record 56 out of 59 Scottish Westminster seats and has sought to frame the election campaign as a two-horse race against Theresa May's party.

She said: "Now, more than ever, we need strong SNP voices at Westminster standing up for Scotland against an emboldened Tory government.

"While the polls have narrowed, the Tories are still on course to win the election.

"Labour proved beyond any doubt that they were unable to provide the opposition needed to keep the Tories in check in the last parliament."

She added: "Only the SNP can provide the strong opposition that Scotland needs to protect our schools, hospitals and vital public services from deeper Tory cuts and further damaging austerity.

"And if the SNP win this election in Scotland, it will strengthen the country's hand when it comes to opposing cuts, defending our place in Europe and on choosing our future as a nation."

The party has already set out a number of pledges, including a promise to retain the triple lock on pensions and an "anti-austerity plan" for additional investment in public services.

On Brexit, it has put forward proposals to keep Scotland in the European single market, with Sturgeon insisting support for her party can give her a mandate for a role in the EU talks.

References in the manifesto related to another independence referendum are likely to be the focus of attention.

Sturgeon has already called for a second vote on Scotland's constitutional future to be held between autumn 2018 and spring 2019.

This demand has been rejected by the UK Government, despite support from a majority in the Scottish Parliament.

The First Minister said: "Central to our manifesto are three core pledges which underpin why it is so important for people across Scotland to get out and vote for the SNP next Thursday.

"SNP MPs will always be a strong voice for Scotland, standing against Tory cuts. We will set out a clear plan to end mindless Tory austerity across the UK and to invest in public services.

"While the Tories are set to plunge Britain into Brexit without a clear plan, a vote for the SNP will give us a strong hand in the Brexit negotiations to ensure Scotland's interests - on jobs and our economy - will be heard at the top table."

She added: "Regardless of whether you voted Leave or Remain, a vote for the SNP at this election is a vote to ensure Scotland's interests are protected throughout that process.

"And the SNP will always make the case that Scotland should have the right to make our own decisions on Scotland's future - and stand against any Tory attempts to diminish the powers of our Scottish Parliament or reverse the gains of devolution."