Labour leader Jeremy Corbyn says he can "still be prime minister" as he aims to thwart Theresa May's attempt to run a minority government.
He told the Sunday Mirror: "This is still on. Absolutely."
Labour will set out its own programme for government as an amendment to the Queen's Speech, focusing on austerity and a "jobs-first Brexit," he says.
He told the BBC's Andrew Marr he will call on MPs from all other parties to back his policies instead of Mrs May's.
Shadow foreign secretary Emily Thornberry told Sky News Labour are "absolutely on our toes" to set up an alternative minority government if Mrs May's government falls apart, accusing the Conservative PM of "squatting in Downing Street".
Mrs May is seeking a loose "confidence and supply" arrangement with the DUP's 10 MPs that would allow her to press ahead with a minority government, after losing her Commons majority in Thursday's general election.
The Conservatives could command a majority with the support of the DUP if they manage to to do a deal with the Northern Irish party.
Labour gained 30 seats in Thursday's general election to take its total to 262 seats, but the Conservatives remain the largest party in Parliament with 318 seats. This is more than the total of Labour, Lib Dems, SNP, Plaid Cymru and Green Party. The number needed for a majority is 326.
This would give the Tories the numbers to pass a Queen's Speech on Monday 19 June, which will set out their legislative agenda.
But shadow chancellor John McDonnell said he believes there is a majority in Parliament to maintain the winter fuel allowance and "triple lock" state pension guarantee, two policies the Conservatives proposed changing in their manifesto.
He told ITV's Peston on Sunday: "I believe the DUP is in favour of scrapping the bedroom tax. There's a whole range of issues like that where we think there'll be a majority in Parliament."
Jeremy Corbyn said he did not think Mrs May had any credibility and it was "unclear" what kind of programme the Conservatives would be able to put forward.
He said there was a "possibility" of voting down the Queen's Speech and Labour were going to "push all the way" to achieve that.
Speaking on the BBC's Andrew Marr show, he said Labour would put down a "substantial amendment to the Queen's speech" based on the main policies in its general election manifesto, with an emphasis on Brexit, young people, and austerity.
He said the Brexit content of that amendment would be about negotiating as quickly as possible a "jobs-first Brexit".
Mr Corbyn said his party was "quite ready and able to put forward a serious programme of government", which he said "obviously has massive support in this country."
He also said he believed that the Great Repeal Bill - the Conservative plan to copy across all EU laws into UK law - would now become "history" - and that there would be "something different" in a few weeks' time.
He told Andrew Marr he thought it was quite possible there could be an election later this year, or early next year, which he thought "might be a good thing."
"We can't go on with a period of great instability" he said, adding that the Labour Party was ready to fight another election campaign.
On Brexit, Mr Corbyn said he wanted "tariff-free access to the European market" and to maintain membership of key European agencies, as well as European Convention on Human Rights and European Court of Human Rights but he confirmed he would press ahead with leaving the EU if he became prime minister.
He also suggested he was ready to build bridges with some of the Labour MPs who have opposed his leadership.
Asked if Yvette Cooper and Chuka Umunna - both of whom had been reported to be planning leadership bids if Labour lost seats in the general election - could come back to the front bench, Mr Corbyn said: "I am the most generous person in the world."
Ms Cooper, who was defeated by Mr Corbyn in the 2015 Labour leadership contest, said the Parliamentary party had "changed a lot" since last year's EU referendum and was now fully behind Mr Corbyn.
"We all need to pull together to take on Theresa May and take on the Tories," she told Sky News.
She did not rule out accepting a job in Mr Corbyn's shadow cabinet, but said she did not want to be "presumptuous".
She said the Conservatives' planned deal with the DUP was "dodgy" and "unsustainable" - and Theresa May's position was "not remotely tenable" because she lacked the skills to hold together a minority government, which has to be more open and collegiate.
She said Labour had to be ready for another election "at any time" and warned the party not to "rest on its laurels," saying it had to work on how to win back more seats from the Conservatives.
In an interview with BBC Radio 4's Today programme on Saturday, Chris Leslie, Labour MP for Nottingham East, refused to say whether he thought Mr Corbyn was a credible prime minister.
He said: "We shouldn't pretend that this is a famous victory. It's good as far as it's gone, but it's not going to be good enough."
He said the party had missed an "open goal" in failing to win a majority.
"You've got to convince them of your credibility and that you can move from protesting about the government to being in government," he said.