Thai officials said on Sunday that an "intense and fierce" gun battle has broken out between anti-government Red Shirt protesters and the military in Bangkok.

CNN has reported that the Bangkok metropolitan area and 21 other provinces have been placed under a state of emergency.

CNN also said that the Thai government called on the thousands of protesters massed in Bangkok's Lumpini Park to halt the violence but would not give in to a demand the United Nations mediate between the Red Shirts and government.

Natthawut Saikua of the United Front for Democracy against Dictatorship (UDD) also known as the Red Shirts, said, "We ask the government to ... withdraw troops out of surrounding area. We are ready to enter talks immediately by having the United Nations as mediator for this negotiation."

Government spokesman Panitan Wattanayagorn said the Thai government's policy is not to allow international organizations to intervene in its internal affairs.

The normally bustling capital was "deadly quiet" Sunday aside from what sounded like automatic gunfire, CNN has reported.

A senior Thai government official said, "The government has been under pressure to be more decisive in its action. We have been showing patience and restraint." That, he alleged, upsets those who want the government to take greater action against the protesters.

The Red Shirts' United Front for Democracy has been demanding Prime Minister Abhisit Vejjajiva Abhisit dissolve the lower house of Parliament and call new elections. The Red Shirts support former Prime Minister Thaksin Shinawatra, who was ousted in a 2006 bloodless military coup. (With Inputs from Agencies)