Troops in Thailand have begun cracking down on anti-government protesters, with shooting heard in the capital, Bangkok.

Soldiers and demonstrators clashed in the early hours of Monday as troops moved to secure a major road junction, forcing back hundreds of protesters, the Reuters news agency reported.

Protesters threw stones and retreated to side streets but several were arrested and at least two soldiers were injured.

The crackdown comes after Abhisit Vejjajiva, the prime minister, declared a state of emergency in the city on Sunday following protests on Saturday that forced the cancellation of a regional summit in the nearby town of Pattaya.

It also follows a call for the overthrow of the government by Thaksin Shinawatra, the prime minister ousted in a military coup in 2006 whom the protesters support.