Authorities in Thailand said they are preparing for possible trouble at a rally Saturday by supporters of ousted Prime Minister Thaksin Shinawatra.

The rally comes on the heels of several outbreaks of violence connected to the efforts of a protest group opposed to the current government of Prime Minister Somchai Wongsawat, Thaksin's brother-in-law.

Thaksin, who was toppled in a 2006 military coup and fled to Britain before being sentenced to two years in prison on a conflict-of-interest charge, is to give a speech by video link to thousands of supporters at a stadium in the capital, Bangkok. His critics fear he may inflame tensions.

On Thursday, a grenade attack wounded 10 members of the anti-government People's Alliance for Democracy who have been blocking a main street in Bangkok.

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"We fear that there will be more violent incidents so security officials have been ordered to be on alert," Metropolitan Police Chief Lt. Gen. Suchart Muenkaew said Thursday, adding that there would be at least 600 policemen at the rally, organized by the pro-government United Front for Democracy Against Dictatorship, or UDD.

Jatuporn Phromphan, one of the UDD organizers, said Thaksin "will be talking about the benefits of a democratic system and how the coup has thwarted that."

"This demonstration will be a peaceful show of force by those who support Thaksin and those who support democratic values in Thailand," Jatuporn said.

Concern about what Thaksin will say is widespread.

"The event organizers have claimed that the program will not be provocative," the English-language Bangkok Post said in an editorial. "Should it turn out otherwise, the UDD must be held accountable."

Thai army spokesman Col. Sansern Kaewkumnerd said the military would also be on alert in case the situation spirals out of control.

"If the police ask for help or if the situation appears to escalate toward violence, we would come in to prevent another round of that," he said in a telephone interview.

The UDD is opposed to the People's Alliance for Democracy, which is seeking Somchai's resignation. They charge that Somchai is a puppet of Thaksin, whom they accuse of corrupting Thai politics.

The alliance's militant tactics have sparked increasing tension and violence since it took over the grounds of the prime minister's offices in late August.

On Sept. 2, a street clash between government supporters and opponents left one person dead and several others seriously hurt.

Even greater violence took place Oct. 7, when the anti-government alliance tried to blockade Parliament, and police efforts to dislodge them with tear gas led to running street battles. Two people died and more than 400 were injured.

Thaksin was convicted Oct. 21 of violating a conflict of interest law in a case relating to a real estate deal by his wife, who was acquitted. He had fled to Britain earlier, saying he could not get a fair trial in Thailand.

He is facing an array of other corruption charges.

Prosecutors have said they will seek Thaksin's extradition.