Media playback is unsupported on your device Media caption Protesters are trying to force Thai Prime Minister Yingluck Shinawatra to resign

A blast at an anti-government rally in Thailand's capital, Bangkok, has injured more than 30 people, amid an ongoing political crisis.

The blast took place at a rally led by protest leader Suthep Thaugsuban, who was unhurt.

At least eight people have died since protests, triggered by a controversial amnesty bill, began in November.

The protesters have been blocking major road junctions in Bangkok since Monday and are camped out in some areas.

They want Prime Minister Yingluck Shinawatra, who they allege is influenced by her brother, deposed leader Thaksin Shinawatra, to step down in place of an unelected "people's council".

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Ms Yingluck has called elections on 2 February, but the opposition are boycotting the polls.

The prime minister has called for restraint and so far security forces have sought to avoid clashes with protesters.

But, says the BBC's Jonathan Head in Bangkok, there are well-armed groups on both sides that appear ready to escalate the violence.

Shots fired

A deputy national police spokesman said Friday's incident took place shortly after 13:00 local time (06:00 GMT). Reports suggest an explosive device, most probably a grenade, was thrown from a building.

"The bomb went off about 30m [100ft] from Suthep and then his bodyguards escorted him back to a rally stage," spokesman Akanat Promphan told AFP news agency.

Image copyright AFP Image caption The blast happened at a rally led by Mr Suthep, left, in Bangkok

Most of those caught in the blast were not seriously hurt, but one person had severe injuries, the city's emergency services centre said.

Footage from a local television station showed injured people on the ground as medical crew rushed to help.

In recent days there have been reports of small acts of violence at protest venues, usually in the evening.

Shots were fired at protesters from passing motorcycles north of Bangkok earlier on Friday, with no injuries reported.

Earlier this week, four undercover police officers were captured by protest guards and badly beaten up.

The protesters have been causing significant disruption in Bangkok since Monday, blocking key intersections in what they are calling a shutdown of the city.

They say they will remain in place until the government resigns.

On Wednesday Ms Yingluck offered to discuss postponing the polls, but Mr Suthep boycotted the meeting.

On Thursday, the country's anti-corruption commission said it was investigating Ms Yingluck in connection with a controversial government rice subsidy scheme.

The scheme guarantees Thai rice farmers - key supporters of Ms Yingluck's government - a much higher price than on the global market, but critics say it is too expensive and vulnerable to corruption.

If Ms Yingluck is found guilty, she could be forced out of politics.