MADRID (Reuters) - Spain’s ruling Socialists would win most votes if an election were held today but would not have a majority, while the far-right Vox would see its support rise slightly, an opinion poll showed on Friday.

FILE PHOTO: Spain's Prime Minister Pedro Sanchez holds a year-end news conference after the weekly cabinet meeting at Moncloa Palace in Madrid, Spain, December 28, 2018. REUTERS/Susana Vera

The official poll by the Centre for Sociological Studies (CIS) showed that it would likely be hard for any party, or group of parties, to pull together a coalition that would have a majority of seats.

Spanish politics, dominated since dictator Francisco Franco’s death in 1975 by the Socialists and the conservative People’s Party (PP), have become increasingly fragmented over the past years.

The CIS poll forecast that Prime Minister Pedro Sanchez’ Socialists would win 28.9 percent of the vote, more than any other party but its worst score since taking power in June.

A parliamentary election is not scheduled before 2020, but the Socialists hold fewer than a quarter of the seats and speculation has been rife over the possibility that an early election could be held this year.

Vox would get 3.7 percent of the vote according to the CIS poll, up from 2.5 percent in its survey carried out in November and up from 1.3 percent in October.

That is still well below the 13 percent of votes forecast for Vox by Sigma Dos pollsters in a survey published by El Mundo earlier this week, a sign of how hard it is for pollsters to estimate the far-right party’s popularity.

The anti-immigration Vox unexpectedly won 12 seats in a regional election in Andalusia in December, becoming a kingmaker there.

Vox has been dominating headlines, telling the PP and center-right Ciudadanos, who depend on its votes to rule the region, that it would only back them if they agreed to policy changes, including on laws protecting women against sexist violence, which it says discriminate against men.

The CIS poll sees PP getting 19.1 percent of the vote in an election, unchanged from last month’s poll, while Ciudadanos would drop slightly to 17.9 percent and the far-left Podemos would get 14.9 percent. The rest of the votes would be spread among smaller parties.

CIS describes itself as an independent administrative body. Its surveys are considered in Spain as official opinion polls.