Twenty-eight people were wounded, seven of them seriously, in a blast at an anti-government protest on Sunday afternoon, the second daylight attack using explosives in 48 hours in the Thai capital.
As tensions soar in the city of 12 million an unidentified gunman hours earlier opened fire on protesters at another protest site, seriously wounding one man.
Sunday's blast tore through a protester's compound near the Victory monument in central Bangkok.
Witnesses said they saw what looked like a grenade being thrown from nearby shops.
At least one journalist was among those injured.
The escalating violence has renewed speculation that Thailand's powerful military will intervene to end the crisis that has left nine people dead and hundreds injured during two months of protests that are dragging down South-East Asia's second largest economy.
Since another explosion in the middle of a protest parade on Friday the numbers of protesters occupying key intersections across the capital have dropped significantly.
A 46 year-old protester died of his wounds and 35 others were injured in that blast that prompted authorities and demonstrators to blame each other.
Police said they are seeking two men, one believed to be the aide of a former opposition Democrat party MP who were seen in a video clip of the explosion that is believed to have been from grenade.
The Democrats support the protest movement trying to topple government of prime minister Yingluck Shinawatra, raising suspicion is was a staged attack designed to blame her supporters.
But protest leaders and Democrat officials angrily denied any role.
Thailand's supreme military commander Thanasak Patimaprakorn said the situation had become serious with the country like a patient suffering from cancer who needs immediate attention.
General Thanasak urged all sides to negotiate but conceded there was no mediator to broker an end to the crisis.
"I have only one wish now which is that everyone sit down and talk and that they are all safe," he said.
"This is the military's stance at this time."
The military has staged 18 coups or attempted coups since the 1930s.
- Fairfax Media