David Willis reports from the thick of the riots

It is the first time since demonstrations for political change began last month that the protests have ended in violence.

Police used tear gas and water cannon after a large crowd gathered chanting for reform.

Some protesters were forcefully removed by plain clothes officers

The protesters responded by throwing rocks and stones, and a series of clashes followed.

Police in balaclavas chased people through department stores, beating some of them.

The city's police chief said his men had seized several petrol bombs and hundreds of pamphlets calling for reform.

The BBC Kuala Lumpur correspondent says the authorities are clearly determined to clamp down on any form of dissent, with an Asia-Pacific summit due to be held in the Malaysian capital in three weeks.

Chemical irritant

Protesters were sprayed with a mix of water and chemical irritant

The worst trouble began after evening prayers in the Kampong Bahru district of the city.

Pro-reform demonstrators threw stones and rocks at the police, who responded by firing tear gas and water cannon containing a powerful chemical irritant to break up the demonstration.

Protestors later regrouped in another location and again water cannon was used to disperse them.

Some of the demonstrators regrouped, and there were violent scenes as police - some plain clothed, others in balaclavas - arrested people in the crowd, including several women.

David Willis in Kuala Lumpur: "I was caught up in this"

Demonstrations in support of Mr Anwar have been declared illegal and several people were arrested in a series of anti-government rallies that followed Mr Anwar's detention.

Most were since released on bail, but police are now warning those who join the protests that they could face arrest under the Internal Security Act, which allows for indefinite detainment without trial.

Anti-government protesters braved the threat of arrest

Mr Anwar was sacked by the Prime Minister, Dr Mahathir Mohamad, last month. He was later arrested, after which, he says, he was beaten by police.

He faces trial next month on four out of 10 counts of corruption and sodomy - charges he says are part of a high-level political vendetta.

One of the two main witnesses against him now says he was stripped, humiliated and brainwashed in custody before telling police he had committed sodomy with Mr Anwar.