The rally went on after the explosion. A man captured by PAD guards for allegedly throwing the bomb near the back of the stage, was taken under police custody. One of the injured was a woman and another was a boy who was badly wounded in the leg, witnesses said.

Thousands of people joined the rally, the first since the PAD set up its New Politics party. The explosion occurred when PAD and New Politics leader Sondhi Limthongkul was addressing his supporters and lambasting arch-rival Thaksin Shinawatra over the Thai-Cambodia row.

A plan was also mooted yesterday to give a Bt10-million award for Thaksin's arrest, with funds to be mobilised primarily from PAD supporters.

Thaksin's "betrayal" - his activities leading to the worsening Thai-Cambodian row - was the focus of the rally, which was peaceful until the explosion. The PAD reiterated its ultimate objective of protecting the monarchy and in a statement called on Cambodia to end the Thaksin-driven hostility and join efforts to restore friendly relations between the two countries. The bomb attack took place despite hundreds of policemen being deployed and bomb experts searching for explosives around the rally site.

Meanwhile, Deputy Prime Minister Suthep Thaugsuban yesterday said the Thai-Cambodian situation was not a cause for concern regarding safety of Thai expatriates there. He also vowed that the Thai citizen charged with spying and held in a Phnom Penh prison would receive due justice as guaranteed by international law.

"If necessary, the government stands ready to provide confirmation that the flight plan is not classified information and that the flight in question was known before the arrest of the Thai air-traffic controller," he said.

The Foreign Ministry and the Thai company operating air-traffic control services at Phnom Penh International Airport will provide legal assistance to Siwarak Chothipong, accused of leaking the flight plan of fugitive ex-premier Thaksin Shinawatra.

"Even though the government is in no position to meddle with the Cambodian judicial process, the charge will likely be dropped in light of the evidence," he said.

Talks with Cambodia to mend fences at this juncture were unlikely to resolve any differences, he said.

The Cambodian government should take the welfare and benefits of the peoples of the two countries into consideration instead of acting on a whim to vent its displeasure at the Thai administration, he said.

The rumour of the arrest of another Thai spy, reportedly working in Siem Reap under Thailand's Armed Forces Security Centre, was unfounded, he said.

Thai citizens should remain calm and not act hastily, he said, adding that the future of Thai-Cambodian ties hinges on whether Cambodia would adjust its stance toward Thaksin, he said.The Foreign Ministry plans to lodge its strongest protest if Cambodian authorities file false and trumped-up charges against Siwarak, said Chavanond Intarakomalyasut, secretary to the foreign minister.

Cambodian authorities dismissed the consular request from Thai charge d'affaires Chalothorn Phaovibul to visit Siwarak in his prison cell on grounds that it was the weekend, he said.

In a telephone interview from Phnom Penh, Chalothorn said Siwarak was detained at a Phnom Penh prison.