The ruling Socialists of Spain (PSOE) won the most seats in Sunday's elections, but fell out of the majority ̵
The Conservative People's Party (PP) came in second and Right Vox more than doubled to become the third most powerful party in the country.
This is the fourth general election in Spain in as many years.
A previous vote in April ended with a clear majority and the Socialists failed to form a coalition government.
This time the Socialist Party won 120 out of a total of 350 seats – three fewer seats than the April vote. PP has 88 seats, up from 66 in the previous poll, while Vox has 52 up from just 24 in April.
Addressing supporters of the Socialists after the results came, incumbent Prime Minister Pedro Sanchez said his priority was "to form a stable government and make policies for the benefit of the majority of Spaniards."
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"I would like to call all political parties because they must act generously and responsibly to unblock Spain's political situation," he added. failing to form a government, Mr Sanchez hoped that calling another election would strengthen his party's arm – but Pablo Iglesias, leader of the left Podemos, warned that he had only strengthened the far right.
"Once again, we are reaching out to the Socialist Party and Pedro Sanchez," he said, adding that he was ready to start negotiations with the party as early as Monday.
Podemos is the natural political ally of the Socialist Party. However, the coalition between the two will not yet reach the 176 seats needed by the majority.
Meanwhile, the center-right Ciudadanos Party – or the Citizens – has gained support, winning just 10 seats this month, up from 57 in April.  Ciudadanos was also overtaken by the ERC-Sobiranistes, an electoral coalition of the Pro-Catalan separatist parties.
Albert Rivera, leader of Ciudadanos, says: "The Spanish want more Sanchez for this legislature, but the Spaniards also want more Vox and less from the political center."
Vox is believed to have benefited from the Catalan crisis newsletter and strong anti-separatist sentiment in other regions of Spain.
"Today, a patriotic alternative and a social alternative that requires national unity to restore constitutional order in Catalonia is consolidating in Spain," Vox leader Santiago Abascal told crowds after the election. Not a Good Night for the Socialists
Guy Hedgeco, Madrid
Although the Socialists of Pedro Sanchez emerge as winners, suffering only minor losses in this election, the overall result is not positive for the incumbent prime minister.
As Podemos lost some ground and Mash Pais secured only a handful of seats, there is no clear left majority. The Socialist right-wing rivals, PP, have recovered many of the seats they lost in the April vote.
If the longstanding political stalemate in the country is overcome, Mr Sanchez may need to seek the support of the PP, or else a third year's election may be required.
Meanwhile, the huge tide of the nationalist Vox Party makes it the country's third political power and it will now be easier to set the agenda on the right. This is likely to prevent Mr Sanchez's attempts to seek a conciliatory solution to the Catalan crisis.
The April elections ended in a deadlock, with parties failing to form a coalition by the September deadline, thus forcing Sunday's elections.
Analysts suggest that in order to form a coalition now, they must form alliances with smaller nationalist parties
Meanwhile, PP and Vox may seek to maximize their profits.
A PP politician said that Prime Minister Sanchez should "start thinking about how to go," given the early results.
What do they say about the far right?
The huge jump in Vox seats will be one of the biggest talking points of the night.
Spain seemed immunized against a wave of far-right populism that has spread throughout the continent over the last decade, with many remembering the military dictatorship of General Francisco Franco.
But now Vox has established itself as a major force in Spanish politics.
France's far-right party leader, Marin Le Pen, took to Twitter to congratulate "the stunning advance of Vox". . Italian populist Matteo Salvini also talks about his pleasure at seeing Vox's success.
"It is not at all racism and fascism. In Italy, as in Spain, we just want to live peacefully in our own home, ”he tweeted.