The aftermath of the blast which hit an area where demonstrators had set up camp
An explosion in Bangkok has killed at least one anti-government protester and wounded more than 20.
The pre-dawn blast rocked an area where demonstrators had set up camp in the city's Government House compound.
Protesters from the People's Alliance for Democracy (PAD) group have occupied the area since late August.
They are demanding the resignation of Prime Minister Somchai Wongsawat's government, saying it is too close to ousted former PM Thaksin Shinawatra.
The demonstrators said a grenade had exploded near the main stage of their protest site at about 0330 (2030 GMT Wednesday).
The protests have seen some of the worst street violence since pro-democracy activists challenged Thailand's army in 1992.
Abuse of power?
The PAD has proved a remarkably resilient movement, says the BBC's Jonathan Head in Bangkok, forcing the resignation of a prime minister and two cabinet ministers, and nearly provoking a military coup.
Anti-government rallies have been held in Bangkok for months
While the protesters have been targeted by small bomb attacks in recent weeks, the latest explosion could herald the start of more aggressive efforts to dislodge them, our correspondent adds.
An alliance of conservative and staunchly royalist academics, activists and business people, the PAD accuses Mr Somchai and his recently-ousted predecessor, Samak Sundaravej, of simply being proxies for Thaksin.
The PAD wants to replace Thailand's one-man, one-vote system with one in which some representatives are chosen by professions and social groups rather than the general electorate.
Thaksin, Mr Somchai's brother-in-law, was forced from office in a military coup in 2006 and remains in exile overseas.
The new government says it wants to start negotiations with the PAD. But it is also pushing ahead with controversial plans to amend the constitution - a key grievance of the protesters who see it as part of a plan to rehabilitate Thaksin.
It accuses him of corruption and abuse of power while he was in office, and has suggested he and his allies have a hidden republican agenda - a serious charge at a time when the country is beset by anxiety over the future of the monarchy.
Thaksin was last month convicted in absentia of violating conflict of interest rules, and still faces several other charges.
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