HANOI (Reuters) - One of Vietnam's highest-ranking leaders has been forced to quit from her posts, the ruling Communist Party said on Thursday, the third top official to exit in two months, as the ruling party proposed a reshuffle of its ranks.

The changes at the top of the one-party state follow weeks of political upheaval during which the chairman of parliament and the country's president both quit over unspecified accusations of wrongdoing, amid an escalating anti-corruption campaign.

Thuong Thi Mai, 66, was accused by the party of "violations and shortcomings," without elaborating, according to a statement.

She was fifth in Vietnam's leadership hierarchy and the only female in the powerful Politburo, Vietnam's elite decision-making body. She was also a permanent member of Party Central Committee's Secretariat.

With her departure, only two of the top five leaders are still in their jobs, including the party chief and the prime minister.

During a meeting on Thursday of the party's central committee, it named four new candidates for the Politburo, which has 18 statutory members. With Mai's dismissal it had been left with only 12 members.

It also said it would propose to the national assembly new candidates for house speaker and president, without naming them.

Parliament is expected to vote on those in a regular session starting on Monday, plus the four Politburo members.

Those include Nguyen Trong Nghia, 62, who heads a 10,000 strong cybersecurity unit and is the party's propaganda chief and former central bank governor Le Minh Hung, 53.

(Reporting by Phuong Nguyen, Khanh Vu and Francesco Guarascio; Editing by Martin Petty)