A grenade blast wounded 46 anti-government protesters in Bangkok, hospital officials said on Sunday, the latest escalation in the country's increasingly violent political crisis.
Police said the blast happened near a stage set up for rallies in front of Government House, the latest in a string of explosions at the site which has been occupied by activists since August.
A spokeswoman for the Erawan Medical Centre said at least 46 people had been wounded.
A spokesman for the anti-government satellite television channel ASTV told Reuters the grenade landed near the Prime Minister's offices, occupied by anti-government group People's Alliance for Democracy.
Channel 3 television showed footage of the wounded being rushed to hospital in pickup trucks. It said at least two people were in critical condition.
"I had come down from the stage about 30 minutes before the grenade dropped into a crowded area," PAD leader Suriyasai Katasila told Channel 3.
He blamed pro-government supporters for the attack, which came as the PAD's dramatic blockade of Bangkok's Suvarnabhumi international airport entered its fifth day.
Protesters force police to abandon checkpoint
Hundreds of anti-government protesters forced several dozen Thai riot police to abandon a checkpoint on Saturday as they tightened their siege of the country's main airport, witnesses said.
About 2,000 anti-government protesters forced back about 150 police from 1km north of Suvarnabhumi Airport, although the incident passed off without violence.
A state of emergency has been declared at Suvarnabhumi international airport and the smaller Don Mueang airport, which the People's Alliance for Democracy (PAD) have taken over.
At Suvarnabhumi hundreds of riot police have moved into place. Police have not yet moved to break up the protests but have said they are prepared to take "other steps" if negotiations failed.
Both airports have been paralysed by the protests and thousands of passengers are stranded in Bangkok, including hundreds of Thai Muslims trying to travel to Saudi Arabia for the Hajj pilgrimage.
The People's Alliance for Democracy say they will not leave until Prime Minister Somchai Wongsawat resigns, which he has refused to do.
The protesters are seeking to oust Mr Wongsawat in the latest escalation in a long-running political crisis. The loose alliance of royalists, businessmen and the urban middle class claims the government is corrupt and hostile to the monarchy.
A day after their police chief was sacked for mishandling the protests, commanders on the ground said they would not yet try to evict by force the thousands of protesters at Suvarnabhumi and Don Muang airports.
But PAD supporters were taking no chances and on Saturday deflated the tyres of ambulances and police vehicles at the police checkpoint. Several vehicles were left stranded in the middle of the road.
In a televised address on Thursday night, Mr Somchai said the PAD members barricaded at the airports were doing massive damage to the economy, but he would avoid violence to end the protests.
The airport sit-ins have forced hundreds of flights to be cancelled, stranded thousands of foreign tourists and grounded millions of dollars of air cargo.
The government began shuttling thousands of stranded tourists by bus to U-Tapao, a Vietnam War-era naval airbase 150km east of Bangkok, as an alternative landing site for airlines, but travellers reported delays and confusion.
The BBC reports the airport closures will cost the country about $US4 billion in lost business and cause serious damage to its reputation as a tourist destination.
The government has said that Mr Somchai will remain in the northern city of Chiang Mai indefinitely for his own safety.
The BBC reports Mr Somchai has already lost the confidence of his army chief, General Anupong Paochinda, and rumours of a coup are circling in the capital.
Earlier this week, General Anupong urged Mr Somchai to call a snap election as a way of easing the crisis.
Thailand has been in political turmoil since former Prime Minister Thaksin Shinawatra was ousted in a military coup in 2006.