Protesters at the anti-government rally on Nov 24 will definitely not lay siege to the parliament, Pitak Siam group leader Boonlert Kaewprasit said on Thursday.
Gen Boonlert, also known as Seh Ai, said if anyone at the rally broke into the parliament compound and the situation became violent he would take responsibility.
A censure debate is scheduled in the parliament from Nov 25 to 27, followed by the vote on a no-confidence motion on Nov 28.
Seh Ai said the rally would not be prolonged. He expected it to last no more than two days and one night.
Gen Boonlert also said he did not believe a "third-hand" would interfere in what he described as a fight between the Pitak Siam group and fugitive former prime minister Thaksin Shinawatra.
The rally would be his last, he said. Either the government would go, or he would.
He denied claims that the rally was being funded by the same group who financed the Sept 19, 2006 coup that toppled the Thaksin Shinawatra government, or with money from illegal casinos or the drug trade. The rally would be purely voluntary, he added.
The Pitak Siam group was preparing a letter to be submitted to Asean and United States President Barack Obama confirming that the rally would be peaceful.
A spokesman for the group said the rally would remain strictly within the scope of the law and would not cause trouble to the public.
The Pheu Thai Party has asked the Constitution Court to order a halt to the planned anti-government rally.
The request was made in a letter submitted by Pheu Thai member Singthong Buachun, who was accompanied by party lawyer Picha Wijitsin.
Mr Singthong said the planned rally was an offence under Section 68 of the constitution since it was intended to topple a democratically-elected government led by Prime Minister Yingluck Shinawatra.
The letter was accept for consideration by Panya Udchachon, deputy secretary-general of the Constitution Court.
Pol Gen Adul Saengsingkaew, the national police chief, has issued an order prohibiting police from taking part in the protest, warning they would face severe disciplinary action.
Deputy police spokesman Thana Chuwong said the order instructed police commanders at all levels to make sure their subordinates understand that joining the rally would be a violation of Section 68 of the charter.
Violators of this order are liable to administrative and disciplinary action, Pol Maj-Gen Thana said.