MADRID — Spain appears headed for political gridlock after Sunday’s inconclusive national elections left parties on both the right and left without a clear path toward forging a new government.

The conservative Popular Party won the elections, but it fell short of its hopes of scoring a much bigger victory and forcing the removal of the Socialist prime minister, Pedro Sánchez. Instead, the party led by candidate Alberto Núñez Feijóo performed below the expectations of most campaign polls.

Even though Mr. Sánchez’s Socialists finished in second place, they and their allied parties celebrated the outcome as a victory since their combined forces gained slightly more seats than the Popular Party and more conservative parties. The bloc that could likely support Mr. Sánchez totaled 172 seats; the right bloc behind Mr. Feijóo, 170.

“It was a Pyrrhic victory for the Popular Party, which is unable to form a government,” said political analyst Verónica Fumanal, adding the conservatives will now have to reach out to the far-right, and even then it won’t be enough. “I see a deadlock scenario in the Parliament.”

The closer-than-expected election was likely to produce weeks of political jockeying and uncertainty over the country’s future leadership. The next prime minister only would be voted on once lawmakers are installed in the new Congress of Deputies.

But the chances of Mr. Sánchez of picking up the support of 176 lawmakers — the absolute majority in the Madrid-based Lower House of Parliament — needed to form a government are not great either. 

The divided results has made the hardline Catalan separatist party Junts,  or Together, emerge as Mr. Sánchez’s potential kingmaker. If Junts asks for a referendum on independence for northeast Catalonia, that would likely be far too costly a price for Mr. Sánchez to play.

“We won’t make Pedro Sánchez PM in exchange for nothing,” Míriam Nogueras of Junts said after the results left her party holding the keys to power.

With 98 percent of votes counted, the Popular Party is on track for 136 seats. Even with the 33 seats that the more conservative Vox party is poised to get and the one seat going to an allied party, the Popular Party would still be seven seats from the absolute majority.

The Socialists are set to take 122 seats, two more than they had. But Mr. Sánchez can likely call on the 31 seats of its junior coalition partner Sumar, or Joining Forces and several smaller forces to at least total more than the sum of the right-wing parties.

“Spain and all the citizens who have voted have made themselves clear. The backward-looking bloc that wanted to undo all that we have done has failed,” Mr. Sánchez told a jubilant crowd gathered at the Socialists’ headquarters at Madrid.

A Popular Party-Vox government would have meant another EU member has moved firmly to the right, a trend seen recently in Sweden, Finland, and Italy. Countries such as Germany and France are concerned by what such a shift would portend for EU immigration and climate policies.

Vox, which had hoped to force its way into power much as other rightist parties have done in other European countries, saw its support fall by 22 seats compared with four years earlier.

Vox’s leader, Santiago Abascal, said that the Socialists’ results amounted to “bad news for Spaniards.”