Supporters of former Thai prime minister Thaksin Shinawatra announced plans on Friday for a mass rally on the third anniversary of the military coup that toppled him.
The United Front for Democracy against Dictatorship (UDD) said it would demand the resignation of Prime Minister Abhisit Vejjajiva at its rally on Sept. 19.
"We will commemorate the coup," Veera Musikapong, a UDD leader, told a news conference.
Known for its red shirts, the group postponed a rally planned for Aug. 30 after the government imposed a tough security law allowing the military to respond swiftly if protests turned violent, without the need to declare a state of emergency.
The security law was not extended after it expired on Tuesday. But Deputy Prime Minister Suthep Thaugsuban told reporters the government would monitor the protest plans and enact the law again if it felt there was a "threat".
Veera said the red-shirted protesters would gather regardless of whether the military invoked the law, which allows soldiers to cordon off Government House, where Abhisit and his Cabinet work.
A three-week occupation of the premier's office by the UDD in April triggered Thailand's worst street violence in 17 years and rattled foreign investors and tourists.
The prospect of more demonstrations could revive concerns over the stability of Southeast Asia's second-biggest economy and Thailand's four-year political crisis, which has already triggered one downgrade of the country's credit rating.
The latest protest will also target General Prem Tinsulanonda, an elderly former prime minister who is now chief adviser of revered King Bhumibol Adulyadej.
Thaksin's supporters accuse the 89-year-old president of King Bhumibol's privy council of helping to engineer the 2006 coup that toppled the billionaire former telecommunications tycoon. Prem denied any involvement.
Prem's residence is only a stone's throw from the Royal Plaza, a big open square where Thaksin's supporters will gather.
"We will end our rally and disperse in the morning of the next day," UDD spokesman Nattawut Saikuar told reporters.
If enough protesters show up, they will gather in front of Prem's residence, he added.
Prem's house was the scene of a bloody riot in July 2007, when thousands of angry "red shirts", armed with steel pipes, clubs and bricks, clashed with anti-riot police in a night-long battle, injuring more than 100 police officers and protesters.
Güncelleme Tarihi: 05 Eylül 2009, 14:22