Spain's acting Prime Minister Pedro Sanchez said Monday that far-left party Podemos had withdrawn from talks on forming a new government, a week before he faces a confidence vote in parliament.
Sanchez's Socialist party won 123 seats in April polls, the most by any party but short of an absolute majority in the 350-seat assembly.
To be sworn in for another term, he needs the backing of Podemos, which won 42 seats, and that of smaller regional parties.
Sanchez faces a confidence vote next Tuesday on his bid to form a new government, but in an interview with radio Cadena Ser he said Podemos leader Pablo Iglesias has "unilaterally broken" off talks.
"We are talking about the complete closure of the door to any kind of negotiation," he added.
Podemos wants portfolios in the new cabinet.
Sanchez initially refused, but softened his stance in recent days saying some posts could go to people with specific technical qualifications. He claimed Iglesias rejected this offer.
Pablo Echenique, a senior Podemos figure, said he was "surprised" by Sanchez's "hard tone".
The Socialists "never wanted to seriously negotiate a coalition government," he said in an interview with private television La Sexta.
Even with Podemos's support, Sanchez is likely to fall short of an absolute majority in next week's vote.
He would then face a second confidence vote two days later when he will require only a simple majority -- more "yes" than "no" votes.
With this in mind, Sanchez has repeatedly called on the conservative Popular Party and the centre-right Ciudadanos to abstain from voting to make it easier for him to be sworn in on a second vote.
If Sanchez loses the second vote, a two-month period would open during which parties would have to resolve the stalemate -- failing which new elections would be automatically triggered.
These would be Spain's fourth general elections in four years.