A small blast hit Thailand's customs department compound on Saturday, authorities said, ahead of a planned street protest by tens of thousands of anti-government campaigners.
The explosion was the latest in a series of about a dozen blasts, mostly caused by grenades, that have been set off in Bangkok and surrounding areas since the rolling demonstrations
began on March 14.
Police said an explosive went off outside the government building in central Bangkok, shattering windows and damaging a van parked nearby, but caused no injuries.
"The bomb went off at 3:45am, we still don't know type of bomb it was, we will have to wait for a forensic examination," said a district police officer.
Red-shirted supporters of ousted premier Thaksin Shinawatra were gathering on Saturday before setting off on a new street parade as they continued their campaign to push for fresh elections.
The "Red Shirts", largely from poor northern areas, say the government is illegitimate because it came to power with army backing in a 2008 parliamentary vote, after a controversial court
ruling removed Thaksin's allies.
