The far-right party says it has "the right and the duty" to be part of a new government in Castile and Leon after winning 13 seats in Sunday's early vote.
Spain's far-right Vox party has made a breakthrough in Sunday's early election in the north-western Castile and Leon region, gaining a dozen new seats by finishing third with 17.6% of the vote.
The conservative People's Party (PP) finished first without gaining an overall majority. With almost all the votes counted, the Partido Popular won 31.4% of the vote, ahead of the Socialist Party (PSOE) of Prime Minister Pedro Sanchez, on 30%.
The PP took 31 seats out of 81 in the regional parliament in Castilla y León, far short of the absolute majority that would allow it to govern alone, with the Socialist Party winning 28 seats. Vox's tally shoots up from one seat previously, to a total of 13.
The result is "historic", said the far-right party's leader, Santiago Abascal. It gives Vox "the right and the duty" to participate in "the formation of a government", he claimed, hinting at an alliance with the PP.
The current president of Castile and Leon and PP leader, Alfonso Fernández Mañueco, said for his part that he wanted to "dialogue with everyone".
A marginal political force barely four years ago, Vox caused a political earthquake in Spain at the end of 2018 by entering a regional parliament for the first time, in Andalusia in the south. The party then became the third political force in the Spanish parliament the following year.
Vox already supports the ruling PP in Andalusia and the Madrid region, without being part of the government. In Castile and Leon, the far-right party has made it known in recent weeks that it will not be content to support the executive from the outside.
The early elections were called in December by Alfonso Fernández Mañueco, who hoped to strengthen his majority in the regional parliament, after breaking with his allies in the centre-right Ciudadanos party.
Continuing to lose momentum following several polls, Ciudadanos obtained only 4.5% of the vote on Sunday and retains only one seat in parliament, down from 12 previously.
In Spain, the regions have broad powers and regional elections take on a national dimension. Pedro Sánchez has also gone on several occasions to support his party's candidate, as have the leaders of the other main Spanish parties.
With a population of nearly 2.4 million, Castile and Leon, a very rural region, has been a stronghold of the PP for 35 years.