MADRID (Reuters) - Spain's ruling Socialists lost some of their advantage over the conservative People's Party in terms of voting intentions in a national election due later this year, while a new leftist platform appeared to gain traction, an opinion poll showed.
While other recent surveys put the PP in front, the poll by the state-owned Centre for Sociological Studies released on Thursday still showed the Spanish Socialist Workers' Party (PSOE) of Prime Minister Pedro Sanchez taking 30.4% of the vote, down from 32.7% a month ago.
Its main rival polled at 26.1% after also losing some ground, but the gap between them diminished to about 4 points from 5 points.
Opposition parties have criticised CIS over what they see as possible bias as the pollster is state-owned and headed by a Socialist.
Meanwhile, the survey showed the leftist electoral platform Sumar launched this month by Labour Minister Yolanda Diaz, on 10.6% of voting intentions, surpassing the junior partner in the Socialist-led ruling coalition Unidas Podemos, almost four points down at 6.7%.
It is still unclear whether Unidas Podemos will join Sumar or compete against it for left-of-centre voters, an option that could potentially reduce seats for the left.
All polls point to a fragmented parliament where no party would have a sufficient majority to govern alone, so smaller parties both on the left and on the right could be crucial.
Far-right Vox ranked the third-strongest political force with 11.1% of voting intentions, up from 10% a month ago.
The only potential option analysts see for the PP to be able to govern would be via an alliance with Vox, untested at the national level and likely problematic, while a new alliance on the left is seen as more likely.
(Reporting by Emma Pinedo, editing by Andrei Khalip and Angus MacSwan)
