Spain’s PM Mariano Rajoy has said his Popular Party has a “responsibility” to try to form a cabinet, despite failing to win a majority in Sunday’s poll.
The conservatives took most votes, but the traditional Popular Party-Socialist two-party dominance was broken by two newer parties.
The Socialists and one of the two new parties have already ruled out supporting a cabinet led by the PP.
The uncertainty prompted a fall on Monday in the Madrid stock market.
Shares on the Ibex 35 fell 2.8% in early trading, before recovering slightly.
“The Popular Party believes it has a responsibility and a mandate to start a dialogue and explore the viability of a stable government that can offer the necessary certainty inside and outside Spain,” Mr Rajoy told reporters.
The comments came after the prime minister met PP leaders.
The PP took 28.72% of the vote in Sunday’s election, the Socialists (PSOE) 22.01%, the anti-austerity Podemos party 20.66% and the centrist Ciudadanos 13.93%.
In the 350-seat parliament this translates to: PP (123); PSOE (90); Podemos (69); Ciudadanos (40).
Mr Rajoy earlier said his party was “still the number one force” in Spanish politics.
But Socialist leader Pedro Sanchez said the elections showed that Spain wanted “a move to the left”.
Although he acknowledged Mr Rajoy had won the right to have the first attempt at forming a government, Mr Sanchez made it clear he would not back a Rajoy-led government.
Meanwhile, Podemos leader Pablo Iglesias said he would hold talks with all the political groupings but that these had not yet started.
But he insisted Podemos would “not allow the PP to govern”.
Mr Iglesias also said those who were talking of a “grand coalition” between the PP and the Socialists had failed to recognise Spain was no longer a two-party system.
Echoing this, Ciudadanos deputy leader Jose Manuel Villegas said: “The two ancient parties, the old left and the old right, won’t have power anymore.”
The figures show that finding any workable administration could be a tough task.
An alliance between the PP and the liberal Ciudadanos would not provide enough seats for a majority.
But an alliance of the Socialists and Podemos would fall similarly short.
Doing the post-election sums:
- Grand coalition: Spain has never had a so-called grand coalition that would bring the Popular Party and the Socialists together – and the Socialists said on Monday they would not join a grand coalition
- Coalition of losers: The Socialists could link up with Podemos and Ciudadanos in a move that would echo the outcome of elections in Portugal last month
- Regional solution: The Socialists could also strike a deal with Podemos and smaller regional parties that won just a few seats each, thereby removing the need for a deal with Ciudadanos
The spotlight could fall on the six smaller groupings, who took 28 seats.
The biggest of these is Erc-Catsi, the Catalonian separatists, with nine seats, but there are other regional separatists from the Basque Country and the Canary Islands.
Joining forces with Mr Rajoy might seem unlikely, given he has called regional separatism the biggest threat to Spanish unity in decades.
In line with the Spanish constitution, after talking to each party, King Felipe VI will nominate a candidate for prime minister. This cannot take place until after the new Congress holds its inaugural meeting on 13 January.
The nominee must then win a vote of confidence in parliament. If this fails, another candidate can be nominated and seek parliamentary approval.
If no administration can be formed within two months of the election, another must be held.
The key issues facing the parties – and which dominated the election – are the economy, corruption, unemployment, regional separatism and social inequality.
Mr Rajoy campaigned on a platform of economic progress, having staved off the threat of collapse. The economy is now one of the fastest-growing in the EU.
Unemployment has been cut, but is still at 21%.
Mr Rajoy’s opponents pointed to his harsh austerity measures – big cuts in public spending, tax increases and health reforms – and the suffering they had caused many Spaniards.
The Spanish result echoes similar leftist swings in southern Europe this year. Syriza won in Greece in January. And the success of a leftist grouping in Portugal will also inspire the Spanish left.