With nearly all votes counted, no political party or likely coalition has won enough seats in the Congress of Deputies to declare victory. Both PSOE, the mainstream social-democratic party of Prime Minister Pedro Sánchez, and their conservative opponents PP, fell short of the 176 seats needed for a majority, even when combined with parties likely to ally with them.

The inconclusive result may lead to weeks of negotiation between the parties, or even a new vote later this year.

Vox, a far-right anti-immigration party expected to form a coalition with PP, lost 19 seats, failing to deliver the votes needed to achieve a right-wing block.

Sumar, a far-left coalition expected to support PSOE, finished a close fourth. Their leader, the second deputy prime minister and labor minister Yolanda Díaz, was boosted by a strong debate performance in the final days of the campaign, where she challenged the anti-feminist policies of Vox leader Santiago Abascal.

Both the progressive and conservative blocks will need to gain the support of smaller regional parties if they want to reach a majority of seats.

PP and Vox will need the vote of PNV, a Basque nationalist party that supported a government led by Mr. Sánchez in 2019 and is unlikely to support a right-wing coalition. They will also need the support of two smaller parties with one seat each, Coalición Canaria (CC), a nationalist party from Canary Islands that recently formed a regional government with the vote of PP, and Unión del Pueblo Navarro (UPN), a historical partner of PP in Navarra.

PSOE and Sumar will have to revalidate the support of the parties that voted for Mr. Sánchez in 2019 and will have to seek the backing of Junts, a Catalan nationalist party.

Míriam Nogueras, a Junts candidate in Barcelona, said, “We will not support Mr. Sánchez in return for nothing…our priority is Catalonia, not the governability of the country.”

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