MADRID • Spain's Acting Prime Minister Mariano Rajoy says his conservatives have "the right to govern" after winning more seats in Parliament in a repeat general election, even though they still fell short of a majority.

His Popular Party (PP) was the big winner of Sunday's election, the second in six months, which played out amid the turbulence from Britain's shock vote to leave the European Union.

Throughout the campaign - and with greater insistence after the Brexit vote - the PP hammered away at the need for stability in reaction to the rise of far-left Unidos Podemos, which like Greece's ruling Syriza party, rejects EU-backed austerity.

Mr Rajoy argued that since the PP came to power in 2011, it has brought Spain back to growth and overseen a drop in unemployment - though at 21 per cent it is still the second-highest in the EU after Greece.

The party, which portrayed itself as the guardian of stability, won 137 seats in the 350-strong lower house of Parliament - 14 more than in December and more than what pre-election polls predicted.

All other parties lost votes, seats or both.

The Socialists held on to second place, as in December - although with just 85 seats it was their worst score in modern history.

The Unidos Podemos coalition came third with 71 seats, reversing pre-election expectations that it could leapfrog over the Socialists and replace them as the main left-wing force.

Market-friendly party Ciudadanos finished fourth, as in December, with 32 seats - down from 40, as many of the party's voters moved back to the PP.

"It's been hard, it's been difficult, it's been complicated, but we put up a fight for Spain," Mr Rajoy told a crowd of supporters.

But while the PP boosted its seats, it still faces the same challenges to form a government as after the December polls when Podemos and Ciudadanos uprooted the country's two-party dominance.

Without a majority, it will need to seek the outright or tacit support of other parties to get a coalition or minority government through.

If PP teams up with Ciudadanos, its natural ally, the pair will still not have enough seats to form a majority centre-right government, so they may also need to court the Socialists or smaller regional parties.

But other parties have been reluctant to back the PP, which has been tainted by corruption scandals and anger over high unemployment and its steep public spending cuts.

The general election in December resulted in a Parliament so splintered that parties failed to agree on a coalition, which prompted Sunday's repeat vote. Now Spain's political leaders are under more pressure to form a government.

AGENCE FRANCE-PRESSE