By Andrei Khalip and Emma Pinedo
MADRID (Reuters) - Spain's Socialist party extended its lead in an opinion poll published on Tuesday, which potentially put it on course to challenge for a majority in a snap election days after it failed to persuade lawmakers to confirm it in government.
Party leader Pedro Sanchez has been acting prime minister since April when the Socialists finished first in an inconclusive national election. Last week he lost two parliamentary votes on making that position permanent after coalition talks with far-left party Podemos broke down.
He now has until mid-September to break the political deadlock or face a fresh election on Nov. 10.
Published on Tuesday, the Centre for Sociological Studies' (CIS) July survey of voter intentions put the Socialists at 41.3%, up from 39.5% the previous month and a large jump from the 28.7% it garnered in April.
The last election in which a single Spanish party secured a parliamentary majority under the country's complex electoral system was in 2011, when Mariano Rajoy's conservatives won 44.6%.
CIS said the latest survey represented direct voter intentions and lacked the checks and balances used in compiling projections, which were generally more accurate.
It polled nearly 3,000 people from July 1 to July 11, before the two parliamentary votes.
The Socialists have said they will keep working with all parties to avoid a repeat election - which would be Spain's fourth in as many years - but were no longer prepared to offer a coalition government to Podemos.
In the poll, Podemos inched 0.4 percentage points higher to 13.1%, just behind the conservative People's Party (PP), in second place on 13.7% and unchanged from June.
The centre-right Ciudadanos fell to 12.3% from 15.8% and far-right Vox to 4.6% from 5.1%.
Both mainstream rightist parties have ruled out support for a Sanchez government.
Sanchez became prime minister in June 2018 after Rajoy was ousted in a parliamentary vote of no confidence.
(Editing by Sonya Dowsett and John Stonestreet)