A grenade exploded Friday in central Bangkok, gravely injuring one man.
It was the second such explosion this week, renewing tensions two months after security forces ended a wave of violent political protests. A man described as a rubbish scavenger was being treated for shrapnel in the head.
Government officials said they believe the blasts are related to the protests and intended to destabilize the government. But opposition spokesmen charge they are the work of government supporters and intended to justify a continued state of emergency.
Also Friday, the chairman of the "Red Shirt" protest group that led the demonstrations was released on bail. Veera Musikapong was one of about two dozen protest leaders who have been detained since the protests were broken up in May.
Police said the latest explosion was caused by a grenade that was left with its pin removed in a plastic bag.
The earlier explosion on Sunday killed one person and wounded at least 10 others at a bus stop across from a shopping area in the city's center. That blast occurred in the same area occupied by thousands of anti-government protesters for 10 weeks this spring. Ninety people died in the violence.
Thursday, Thailand's prime minister Abhisit Vejjajiva lifted a state of emergency in six provinces imposed during massive anti-government protests earlier this year.
But the government said emergency rule would remain in effect in Bangkok and nine other provinces where authorities still perceive some danger of unrest.
Mr. Abhisit first declared a state of emergency in April. The emergency decree suspends some civil liberties, allows censorship and makes it easier to use the military to keep the peace.
The Red Shirts are mostly rural poor and urban working class activists who support former Prime Minister Thaksin Shinawatra, ousted in a 2006 coup on allegations of corruption.
They view Mr. Abhisit's government as a puppet of Bangkok's elite and the military, and accuse it of taking office illegally.
Some information for this report was provided by AFP and Reuters.