Spain's caretaker socialist prime minister Pedro Sanchez lost a crunch post-election vote of confidence on Thursday after coalition talks with the far-left failed.

Sanchez faced the vote in parliament after his Socialist party won most seats in an inconclusive general election in April without securing a majority.

On Thursday, apart from the 123 lawmakers of his own party, just one other deputy from a regional grouping supported the Socialist leader, leaving him far from the simple majority he needed to go through.

This moves Spain a step closer to holding its fourth general election in as many years.

Spain faces several challenges: an ongoing separatist movement in its northeastern region of Catalonia, high unemployment, low wages and job insecurity.

Sanchez now has another two months to find ways of getting support, either for a minority or coalition government.

Without a deal Spain would have to go back to the polls in November.

'Ultimately succeed'

Representatives from the socialists and the far-left Podemos party had been working to secure a deal for what would have been Spain's first post-dictatorship coalition government. But talks stalled on Wednesday evening.

Podemos leader Pablo Iglesias "wanted to enter government to control the government," Sanchez told parliament, despite coming fourth in the April general poll.

He said Podemos's proposal entailed "controlling 80% of government expenditure."

Iglesias retorted that Sanchez had done little to negotiate a government since the April general poll.

"It's very difficult to negotiate in 48 hours what you didn't want to negotiate in 80 days," he said.

Both sides had agreed to give Podemos the post of deputy prime minister with responsibility for social issues and the health ministry.

But Podemos also wanted the science and labour ministries, which the Socialist party (PSOE) refused, preferring to give it the housing and equality ministries.

Federico Santi, senior analyst at the think-tank Eurasia, predicted Sanchez's Socialists would "ultimately succeed" in forming a coalition government with Podemos before September after which parliament would be automatically dissolved and fresh elections called.

"There is pressure from both parties' bases to reach an agreement. Parties are also reluctant to risk new elections. Podemos would likely suffer another setback, further undermining its leverage and its internal coalition," he said.

The new government's programme would likely raise pay for civil servants, further increase the minimum wage and introduce a  tax reform that includes raising income taxes on high incomes and corporations and lowering the sales tax for essential items, he said.

'Bad chemistry'

Podemos and the Socialists have accused each other of blocking negotiations as distrust between both sides rides high.

Both sides will have to "work hard for there to be a coalition government" since there is "bad chemistry" between Sanchez and Iglesias, political analyst Manuel Mostaza of consulting firm Atrevia told AFP

But he added "two months is a long time to heal wounds."

The Socialist premier came first in the national poll in April with just 123 parliamentary seats out of 350, forcing him to seek backing elsewhere.

Since 2015, Spain has shifted from a two-party system to a deeply fragmented parliament with the emergence of Podemos, liberal party Ciudadanos and more recently far-right Vox.

That has resulted in minority governments which have been unable to get any major reforms through, and Sanchez was forced to call early elections in February when his draft budget was rejected.

Apart from Podemos's vote, Sanchez also would have needed the backing of several other lawmakers from regional parties.

But even the abstention of key Catalan and Basque separatist parties wasn't enough, as right-wing parties voted against Sanchez.