Riot police take cover during clashes in Ulan Bator July 1, 2008. [Agencies]

The headquarters of the Mongolian People's Revolutionary Party (MPRP) in the centre of Ulan Bator was set alight and looted, according to an AFP reporter and other witnesses at the scene.

Some of an estimated 6,000 protesters from the rival Democratic Party – which claims the MPRP bought votes and used other tactics to win Sunday's election – threw rocks at firefighters arriving to put out the blaze.

Police responded by firing rubber bullets and tear gas but the clashes continued and the violence later spread to other parts of the capital.

A police station was attacked when protesters attempted to free rioters imprisoned earlier in the day.

Part of the Cultural Palace, which contains an art gallery, a museum and a theatre, was on fire early Wednesday as violence continued despite the emergency decree.

Later TV images appeared to show the situation was calmer.

Early reports said 30 policemen and 25 civilians had been injured.