Nicola Sturgeon's offer of SNP support for Labour in a hung parliament was bluntly rebuffed in a fiery TV debate between four Scottish party leaders.

Labour's Scottish leader Jim Murphy said his party didn't need SNP help in bruising clashes in which he called her "a First Minister with a second-rate record".

The two-hour showdown, held by STV in Edinburgh's Assembly Rooms, was the most passionate TV debate of the election campaign so far.

With opinion polls suggesting the SNP is on course for a near landslide and Labour facing the loss of dozens of seats, the pressure was on Mr Murphy to claw back support for his party.

And straight away the Labour and SNP leaders clashed after Ms Sturgeon said: "I don't want David Cameron to be prime minister, I'm offering to help make Ed Miliband prime minister."

Mr Murphy insisted: "Nicola, we don't need your help. What we need is people north and south of the border, people in Scotland, people in England and people across Wales coming together to kick out an out of touch government."

But the First Minister hit back: "The Labour Party right now is not offering an alternative to Tory austerity.

"I stood on a platform last week in the UK leaders debate with Ed Miliband and I heard Miliband say if Labour is elected and left to their own devices there will be further spending reductions."

Mr Murphy said Labour had changed, but added: "I'm not pretending it's easy for Labour, I'm not pretending we have all of the answers."

But Scottish Conservative leader Ruth Davidson gave an impressive performance in the debate and challenged Ms Sturgeon on her plans to support a minority Labour administration.

Ms Davidson asked: "Why is Nicola running around saying 'Labour is rubbish, vote for me so I can put them in office?'"

She ruled out a Tory deal with UKIP, saying: "There will be no deals with UKIP. They won't have enough MPs in parliament, they will not get into double digits in parliament in order to be able to have a coalition deal so there will be no deal.

"I've already said my preference is minority government."

Challenged by a member of the audience about SNP plans for a second referendum, Ms Sturgeon said: "I respect the result of the referendum last year."

She said the General Election was a re-run of the referendum campaign.

But when Bernard Ponsonby, who was chairing the debate, asked her about after the 2016 Scottish elections, she said: "That's another matter," prompting cries of "Oh!" from the audience.

Willie Rennie of the Lib Dems, who was often marginalised during the debate and was by far the weakest of the four performers, said he wanted to maintain the progress his party had made in government in the next five years.

He said: "I don't want to veer off to the left or the right like the others propose. I want to keep on that path and keep that recovery going.

"What we need to do to ensure that we do that is invest in the NHS and make sure we balance the books."

But despite the passion and intensity of the debate there was no clear winner and within 24 hours the four, along with the Scottish leaders of the Greens and UKIP, will do battle again in another TV debate.