Dozens of people have been wounded in Thailand's capital after a grenade was hurled at anti-government demonstrators marching through Bangkok.

Protest leader Suthep Thaugsuban was in the procession but was not wounded when the explosive device was thrown into a truck. Police said the grenade was hurled from a nearby building.

Thailand has been wracked by repeated bouts of unrest since the military ousted former prime minister Thaksin Shinawatra in 2006 amid charges of corruption. Anti-government demonstrators seeking to oust Thaksin's sister, Prime Minister Yingluck Shinawatra, have taken over seven key roads and overpasses in Bangkok, blocking them off with sandbag walls and steel barricades.

The protests, which are also aimed at derailing February's elections, have been peaceful. But small acts of violence have reported nightly, including shooting attacks at protest venues and small explosives hurled at the homes of top protest supporters. It is unclear who is behind them.

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Anti-government protesters help a man injured in a grenade attack during a rally in Bangkok Reuters
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Anti-government protesters carry a man injured in a grenade attack during a rally in Bangkok Reuters
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An anti-government protester prepares to enter an abandoned building to search for the bombing suspect Reuters
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Anti-government protesters search for a suspect inside a deserted building following a grenade attack during a rally in Bangkok Reuters
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Anti-government protesters march during a rally in central Bangkok Reuters
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An anti-government protester on a motorbike pulls caricatures of Thailand's Prime Minister Yingluck Shinawatra and her brother Thaksin during a rally in Bangkok Reuters
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Workers of the Import-Export Bank of Thailand leave after anti-government protesters forced their evacuation Reuters
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Anti-government protesters chain up the door of a meeting room of the Public Health Ministry in Bangkok Reuters
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Riot policemen escort an anti-government protester during clashes at the Thai-Japan youth stadium in Bangkok Reuters
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A protester in Bangkok surveys the scene Reuters
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An anti-government protester gives a donation as others wake up in their encampment built between shopping malls in central Bangkok Reuters
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Thailand's PM Yingluck Shinawatra at a meeting to discuss an Election Commission proposal to postpone the upcoming general election Reuters
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An anti-government protester wakes up in his tent inside the protesters' encampment built between shopping malls in Bangkok Reuters
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Protest leader Suthep Thaugsuban addresses demonstrators occupying a major intersection in central Bangkok Reuters
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Anti-government protesters pose for photographs behind two Thai national flags that were hung to block an entrance to a bridge in central Bangkok Reuters
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A protester holds a bag with money donated to their cause as protest leader Suthep Thaugsuban arrives to speak to his supporters in Bangkok Reuters
Thailand