Officials say 36 people have been injured in Friday’s explosion at a demonstration in Bangkok.
It came after several days of calm in the Thai capital which had suggested the anti-government movement was running out of steam
One analyst has predicted the attack could increase the number of clashes between demonstrators and those loyal to the government and so hasten a military intervention.
The protest leader Suthep Thaugsuban who was unharmed in the explosion was in defiant mood when he addressed a rally after the incident.
“There have been 27 attacks since the beginning of this campaign, two or three people have been killed. Dozens are injured, we are so tired and it is painful but we are not going to step back, we are going to take them down,” he said.
It remains unclear who was behind Friday’s blast though Thaugsuban was quick to point the finger at the government.
Thailand is set to hold elections on February 2. The protesters and opposition leaders have vowed to boycott the poll in their bid to oust Prime Minister Yingluck Shinawatra who heads a caretaker administration.