The ruling Pheu Thai Party has dismissed rumours it was intending to groom Yaowapa Wongsawat, former prime minister Thaksin Shinawatra's younger sister, to take over as prime minister.
The suggestion was made by the Democrat Party following the resignation of Kasem Nimmonrat, an aide to Mrs Yaowapa, as a Pheu Thai MP for Chiang Mai.
The opposition said Mr Kasem's resignation was probably intended to make way for Mrs Yaowapa, the wife of former prime minister Somchai Wongsawat, to return as an MP after being freed from a five-year political ban and take over from Yingluck Shinawatra as prime minister in case Ms Yingluck is disqualified over a loan transaction probe by the National Anti-Corruption Commission (NACC).
Prompong Nopparit, the Pheu Thai spokesman, said Mr Kasem told the party's executive committee and core members that he was resigning for health reasons.
Prime Minister Yingluck Shinawatra helps Pheu Thai Party candidate Kasem Nimmonrat, right, campaign in Chiang Mai's San Kamphaeng district ahead of an MP by-election in Constituency 3 on June 2, 2012 in the province. (File photo)
Mr Kasem said he felt he was more suited to serve the people at a local level than at the national level and insisted he had not been forced to resign by any senior figures in the party, Mr Prompong said.
Mr Prompong dismissed as untrue the suggestion that Mrs Yaowapa would run in a by-election to take Mr Kasem's place and be prepared to take over as prime minister.
He said Ms Yingluck had gained wide recognition from the international community as prime minister and the case against her, which is now with the NACC, had not affected her premiership.
Ms Yingluck is being investigated by the NACC over allegations she lent 30 million baht to a company in which her spouse, Anusorn Amornchat, was a shareholder.
The NACC is looking at whether asset concealment was involved.
Mr Prompong said the party's committee for the upper North chaired by Commerce Minister Boonsong Teriyapirom would be responsible for picking a candidate to run in the by-election.
If Mrs Yaowapa wanted to run in the by-election, she could make a proposal to the committee for consideration.
The party would begin the selection process after the Election Commission announces the by-election date, he added.