Dozens of people have been injured in the Thai capital Bangkok when a grenade blast ripped through a crowd of marching anti-government demonstrators.
The ominous development raises tensions in the country's political crisis and the spectre of more bloodshed to come.
Protest leader Suthep Thaugsuban was in the procession but was not wounded when the explosive device was thrown toward a truck driven by demonstrators that was several dozen metres ahead of him, officials said.
The city's emergency services centre said 36 people were injured, most not seriously, although one man was in surgery.
Witnesses said panicked people began running away after the blast, while some helped carry victims with blood dripping from their arms and legs. A damaged pickup truck sat idle, its front tyres flat and petrol from a ruptured tank spilling across the road near splotches of blood.
Thailand has been convulsed by repeated bouts of unrest since the military ousted former Prime Minister Thaksin Shinawatra in 2006 amid charges of corruption and alleged disrespect for the monarchy. The crisis boiled over again late last year after the ruling party attempted to push through an amnesty bill that would have allowed Mr Thaksin to return from exile.
Anti-government demonstrators seeking to oust his sister, Prime Minister Yingluck Shinawatra, have taken over seven key roads and overpasses in Bangkok this week, blocking them off with walls of sandbags, tyres and steel barricades.
The protests, which are also aimed at derailing February 2 elections that Ms Yingluck called in a bid to defuse the crisis, have been peaceful. But assaults have been reported nightly, including shooting attacks at protest venues and small explosives hurled at the homes of top protest supporters. It is unclear who is behind them.