MADRID - The secretary general of Spain's main opposition People's Party (PP) resigned on Tuesday in a snowballing internal conflict that could further undermine the conservatives' popularity and play into the hands of the rising far-right Vox.

"I have decided to leave the post," the party's No. 2 official, Teodoro Garcia Egea, told La Sexta TV channel late at night.

Garcia Egea became the latest and highest-ranking political casualty in the row that broke out last week, when Isabel Diaz Ayuso, the popular regional leader of Madrid and a potential candidate for the premiership, accused her party's top brass of trying to discredit her.

PP leader Pablo Casado has since faced calls from senior party figures to resign and his leadership is expected to be challenged at an extraordinary steering board meeting called by Casado.

"I am stepping down to facilitate a transition," Garcia Egea said. He added he spoke to Casado in the afternoon and both have decided that his departure was the best decision.

Ayuso says Casado's entourage had been trying to collect evidence of corruption against her and her entrepreneur brother over a contract to buy face masks in the early stages of the pandemic. She denies any wrongdoing.

Earlier on Tuesday, the anti-corruption prosecutor's office opened an investigation into the case.

The rift could further shrink PP's voter base and benefit Vox, which is already the third-largest force in a polarised and fragmented parliament. An opinion poll by SocioMetrica over the weekend suggested that Vox could overtake PP, as Vox garnered 20.9% of voting intentions and PP had 20.1%.

Spain is ruled by a minority leftist coalition government and the next general election is not due until late 2023.

The PP's popularity has dwindled over past decade due to corruption scandals and growing political fragmentation.

  - Reuters