Bangkok - Thai police have arrested three men who they claim were plotting to assassinate an advisor to King Bhumibol Adulyadej at a time of rising political tension in the country, a news report said Wednesday.

   The suspects allegedly told investigators that some military officers wanted to create turmoil ahead of Wednesday's mass rally by supporters loyal to fugitive former prime minister Thaksin Shinawatra, the Nation reported.

   The supposed target was Chanchai Likhitjittha, a member of the royal Privy Council and former Supreme Court judge who Thaksin claimed was deeply involved in the decision to overthrow him in a September 2006 coup. Chanchai later served as justice minister in the military's post-coup government.

   The three men, including the alleged organizer of the plot, an army major, have all confessed, deputy national police chief General Jongrak Chuthanont said.

   The would-be gunman, who was apparently hired for 130,000 baht (3,600 dollars) and told the target was an embezzling businessman, was caught casing Chanchai's home on the outskirts of Bangkok.

   A mass demonstration by Thaksin's Red-Shirt supporters Wednesday is aimed at shaking up the political scene by targeting royal advisors who the group claims are meddling in politics.

   Red Shirt leaders hope at least 100,000 people will gather outside Government House, the cabinet offices, before moving on the nearby home of former prime minister and army commander General Prem Tinsulanonda, the man they claim was the "mastermind" behind the 2006 coup. Prem currently heads the Privy Council.

   News of the alleged plot against the royal advisor was being treated skeptically in some quarters. "A very convenient plot," said a Red Shirt organizer, who asked not to be named.

   Prime Minister Abhisit Vejjajiva said the authorities would act "decisively" to protect the monarchy and maintain law and order during the protest but that no state of emergency would be called.