MADRID (Reuters) -Spanish Prime Minister Pedro Sanchez's Socialist Party (PSOE) lost ground in the latest opinion poll released on Friday, in the wake of a corruption scandal, and a sizeable share of poll respondents said they wanted him to call an election.

Pollsters Db40, who surveyed 2,000 people from June 26 to 30, said support for the PSOE fell to 27% - the party's lowest rating in two years - from 29.8% in its previous monthly survey. The main opposition People's Party was well ahead on 33.3% support.

The PSOE was rocked in early June when police released a report alleging graft by the party's No.3 official Santos Cerdan, who has since been removed from his posts and is now being held in custody.

Sanchez, who leads a minority coalition government comprising far-left party Sumar, has resisted pressure from the opposition to resign and call a snap election. 

On June 30, a judge ordered that Cerdan be held in pre-trial detention, a move that made the situation even more delicate for Sanchez.

Sanchez has apologised and promised to make changes at PSOE, which will be announced during a congress this weekend. But he has said he intends to stay on through the end of the term and to lead the party in the next election in 2027. 

The poll showed 41.2% of those surveyed want Sanchez to call an early ballot, however, while 17.6% want him to step down and let someone else lead the party.

The conservative People's Party appeared to benefit little from the Socialists' decline as the poll showed it gaining just 0.5 percentage points. But the far-right Vox, the third-largest party in parliament, climbed 1.3 percentage points to 15.2%.

A majority of respondents deemed Sanchez's reaction to the crisis, including the firing of Cerdan, as belated and insufficient, although most Socialist voters in the survey said he had acted in a timely and appropriate fashion.

(Reporting by Inti Landauro; Editing by Andrei Khalip and Hugh Lawson)