Two Thai policeman were killed and 13 people wounded in gun and grenade attacks overnight, threatening efforts to forge a deal on ending nearly two months of anti-government protests that have undermined the economy.
Prime Minister Abhisit Vejjajiva has put forward a plan to end the rallies that have crippled Bangkok and scared off tourists, but it remains in limbo as talks drag on over the details, including a proposed early election in mid-November.
Police and an official at the state-run Erawan Medical Centre said the first policeman was killed by a gunman on a motorcycle in a drive-by shooting just before midnight, and the second in a series of suspected grenade blasts around two hours later.
The attacks took place in the Silom Road area of the capital guarded by soldiers and packed with hotels and bars popular with tourists. The area is close to the entrance to a fortified encampment held by "red shirt" protesters since early April.
Protest leaders were quick to condemn the violence, which could add to pressure on Abhisit from the Bangkok middle classes and traditional elite to take a tougher line with the red shirts.
"We were not involved in what happened last night," Weng Tojirakarn, a top red shirt, told supporters on Saturday from the stage set up at the protest site. "We are very sorry and we want to condemn the ones who were behind the attacks."
Abhisit ordered a tightening of security in the area after a meeting on Saturday with Deputy Prime Minister Suthep Thaugsuban and the government's crisis control group, the Centre for the Resolution of the Emergency Situation (CRES).
"CRES believe there are a group of people who don't want the protest to stop," government spokesman Panitan Wattanayagorn told reporters.
The stand-off has paralysed the commercial heart of the capital for nearly two months, but its roots stretch back to the prime ministership of Thaksin Shinawatra - a populist tycoon ousted in a 2006 military coup - and the deep social divisions it exposed between Thailand's traditional elite and rural masses.
The temperature of protests had been cooling after a week of calm following Abhisit's offer to dissolve parliament in the second half of September ahead of an election on Nov. 14 as part of a plan to end a crisis that has now killed 29 people.
But rival camps were still haggling over the details of the plan, with the mostly rural and urban poor red shirts refusing to leave their camp in central Bangkok, where sleek malls and luxury hotels have been forced to close their doors since April 3.
"We want Abhisit to withdraw troops from this area. He has to show sincerity by lifting a state of emergency first," said protest leader Weng. "We agree with the reconciliation plan, but we want Abhisit to say when he will dissolve parliament."
At least 10,000 protesters rallied on Friday night at the heavily barricaded camp covering 3 sq km (1.2 sq miles), and local TV said several thousand more were travelling to Bangkok from their northeastern heartland on Saturday.
Government spokesman Panitan said security forces would try to stop more people joining the protest.
"The move by red shirts to mobilise more protesters in Bangkok could affect how the government officials do their jobs and preparation plan," he said.
Friday's brazen shooting took place just 50 metres from the fortified front lines of the red shirt encampment in a business district packed with hotels, banks and offices close to the city's famous Patpong go-go dancing bars. No arrests were made.
Reuters reporters heard three loud blasts in in the same area about two hours after the shooting.
A hospital official said 13 people were wounded in the violence, three civilians, three soldiers and seven police.
The wounded included two "multi coloureds" protesters among a group of several dozen who had gathered to voice their opposition to the red shirts.
The red shirts, who had demanded immediate elections when their latest protest rally started in mid-March, say the ruling coalition lacks a popular mandate after coming to power in a controversial parliamentary vote 17 months ago.