BANGKOK, Thailand - About 1,200 riot police assembled on Saturday in central Bangkok, waiting for an order from the Thai prime minister who has threatened to forcibly break up an extended anti-government protest.

At least 2,000 protesters defied the threat and continued to block a major avenue in the city's historic district, with some activists fashioning improvised shields and batons out of plywood boards and wooden rods.

The protest by the People's Alliance for Democracy (PAD) began last Sunday, and has at times drawn up to 10,000 people, according to police.

Now the alliance says it wants the newly elected Prime Minister Samak Sundaravej to step down, accusing him of acting as Thaksin's puppet.

"I will not yield to your demand," Samak said in a televised speech early Saturday.

"I have prepared police and military forces. You must find another place to rally that will not affect or violate other people's rights," he said, stressing that obstructing traffic was illegal.

"Who do you want to stage a coup this time? If you want to fight, we fight in parliament," Samak said.

The protest group's leader, media baron Sondhi Limthongkul, vowed to defy the dispersal order.

"PAD will not abandon any of you. I will not run away from death. I want to tell you that whatever happens to me, please take revenge for me," Sondhi told the cheering crowd.

"If government decides to use force to disperse the protest, then we have to defend ourselves and we are ready," PAD spokesman Suriyasai Katasila told reporters.

An aide to Samak, who spoke on condition of anonymity, told AFP that the prime minister would consider declaring a state of emergency if the situation spun out of control.

"If lenient measures fail to break up the rally, an emergency decree would be a last resort," the aide told AFP.

Supreme Commander General Boonsrang Niumpradit told reporters that Samak has yet to issue an order mobilising soldiers, but that the military would comply if an order is given.

"I am convinced that the prime minister will use only police forces. He will only use the military if the situation is very critical, because in most cases the result is tragic," he said.

A police official told AFP that 1,000 reinforcements from nearby provinces were expected to arrive in Bangkok by midnight.

The protest began in opposition to Samak's drive to amend Thailand's military-backed constitution. The kingdom's royalist elite oppose the planned amendments, and the controversy had raised rumours of a new coup.

His government also came under fire over a speech made by a minister attached to the premier's office.

Critics said the speech insulted the nation's revered king by questioning the role of the palace in Thai democracy, a serious criminal offence.

The minister, Jakrapob Penkair, resigned on Friday saying he wanted to ease political tensions. Samak has also agreed to put his plan to amend the constitution to a referendum.