The Democrat leader made clear his stance after the party's former secretary-general Suthep Thaugsuban revealed that convicted ex-premier Thaksin had sent mediators to invite the Democrat party to join the government in exchange for the party not objecting to the attempted rewriting of the Constitution and the passage of a national reconciliation bill.
Mr Abhisit said Mr Suthep kept him informed in a timely manner on the issue and the Thaksin-proposal to form a two-party government.
He said he had already informed the Democrat party executives of the matter.
"I reaffirm that the Democrat party has never had any [such] plan on that and everyone agrees that the party will not join the Pheu Thai-led government but [we] were still contacted," said Mr Abhisit.
Mr Thaksin can do anything for his own benefit and the move might only be an attempt to test the water, Mr Abhisit said.
The Democrat leader said that Mr Suthep's report regarding Mr Thaksin was accurate.
Mr Suthep on Monday stood by his claim, saying he disclosed the details following Defence Minister Sukampol Suwannathat’s claim that no one, including the army, wants to work with the Democrat party.
Mr Suthep said that Mr Thaksin sought negotiations via mediators several times. The first time was in January, mediated by two non-partisan women of high social rank. They invited Mr Suthep to talk with Mr Thaksin in Dubai where he now stays in self-exile, or any country convenient for Mr Suthep.
The former deputy premier said at that time he rejected the invitation and the last contact occurred on June 3 at 5.45pm. He was invited to the home of a prominent figure.
Mr Suthep claimed he was asked that the Democrat party stop opposing the charter amendment and the reconciliation bill, and to stop the Democrat’s ongoing rallies against the government in exchange for participation in the coalition government and ceasing legal action against Mr Suthep and his son over alleged illegal land possession.
The former Democrat executive said he rejected the request and pledged to fight his case in court.
Mr Suthep said he last met Mr Thaksin in 2006, before the 19 September coup, at Phitsanulok House, seeking to ease political deadlock during that period and that they have not met since then.
However, Prime Minister Yingluck Shinawatra dismissed Mr Suthep's claim Monday, saying she has never heard of the matter and that the invitation was ‘impossible’.
The premier said that both parties play different roles under the democratic system; Pheu Thai party is the government while the Democrats have a duty to scrutinise the government's work.
Meanwhile, Pheu Thai MP and key red shirt leader Korkaew Pikulthong dismissed Mr Suthep's claims, saying the invitation is impossible and that the Democrat move is aimed to distance the Red Shirts from the ruling party.
"Mr Suthep's remark is groundless. It's just the Democrats' ploy to sow mistrust among the red shirts against Thaksin and vent their anger against the government," he said. "Mr Suthep sees that the government could be toppled like [those of the] Somchai and Samak administrations if (the Democrats) successfully pit the Red Shirts against the Pheu Thai.”
Mr Korkaew noted that if the negotiations did exist, the Pheu Thai party could be broken.
"A hundred of my fellow red shirts had lost their lives,” he said. “It's impossible that I would join with Mr Suthep."
The Red Shirt leader said he is confident that the ex-premier would not make an alliance with the Democrats as then he could not answer the public.