By Simon Johnson and Johan Ahlander
STOCKHOLM (Reuters) - Social Democrat leader Stefan Lofven has 48 hours to persuade a slighted Left Party, whose support he needs to get elected, to back him as Sweden's prime minister and end four months of uncertainty after a tied election.
The Left Party said on Monday it wanted assurances of a voice in policy in return for backing Lofven, who has support from the Greens, Centre and Liberal parties.
Parliament's speaker, who had been set to nominate Lofven as prime minister, said he would give the parties until Wednesday to sort out a deal.
"The Swedish people want to see a solution and end to all this back and forth," speaker Andreas Norlen said.
"I'm giving them 48 hours to solve these problems and I assume they will do all they can to reach a solution."
September's election delivered a hung parliament and the centre-left and centre-right blocs have been unable to form a government without the support of the anti-immigration Sweden Democrats, a party with roots in the white-supremacist fringe that holds the balance of power.
Lofven looked set to get a second term after agreeing a policy platform with the Centre and Liberals - part of the centre-right Alliance bloc - and Greens, which includes tax cuts and measures to ease rules in the highly regulated labour market.
The deal included a clause explicitly excluding the Left Party from influencing policy.
"They want our votes in order to take power, not to give us any say. That is totally unacceptable," Left Party leader Jonas Sjostedt told reporters.
However, he held the door open for a deal and said Lofven's comments on Monday showed there was movement "in the right direction".
"Our goal is that Stefan Lofven becomes prime minister, but we are not yet at a point where we can vote for him," Sjostedt said.
Lofven said the agreement with the Centre, Liberals and Greens still left room for cooperation in areas outside the budget and a 73-point policy programme.
But he said the four-party deal could not be renegotiated.
"The alternative is not Social Democratic politics, it is Moderate, Christian Democrat government that relies on the Sweden Democrats," Lofven said.
The speaker said he would nominate a candidate for prime minister on Wednesday with a vote to be held on Friday.
If parliament rejects that candidate, the speaker said a final vote will be held next week before triggering snap elections.
GRAPHIC - Election scenarios: https://tmsnrt.rs/2p45tJh
(Additional reporting by Johan Sennero; editing by Niklas Pollard and Robin Pomeroy)