BANGKOK — Thai authorities say they have abandoned a plan to impose curfew in parts of Bangkok where 25 people have been killed in four days of clashes.Lt. Gen. Aksara Kerdphol, the army's assistant chief of staff, toldreporters Sunday that the government no longer saw a need to enforce acurfew.The army had said earlier that a curfew would be imposed later in the day.Aksara did not explain the reversal.Thailand's Red Shirt protest leaders said Sunday they are willing to negotiate with the government if the army ends its crackdown immediately to put an end to four days of street fighting that has killed 25 people."We are willing to negotiate immediately. What's urgent is to stop the deaths of people. Political demands can wait," Nattawut Saikua, one of the leaders, told reporters and supporters."The government must order a cease-fire and troop withdrawal first, then we will ... call back our people who are outside," he said, referring to hundreds of Red Shirt militants who have been fighting Thai troops.However, Nattawut said the UN must serve as a mediator in the talks because "we don't see any neutral and just organizations."There was no immediate response to the offer from the government, but it raised a glimmer of hope for ending the violence.The deadly clashes have raised concerns of sustained, widespread chaos in Thailand — a key U.S. ally and Southeast Asia's most popular tourist destination that promotes its easygoing culture as the "Land of Smiles."A towering column of black smoke rose over the city Sunday as protesters facing off with troops set fire to tires serving as a barricade. Elsewhere, they doused a police traffic post with gasoline and torched it as sporadic gunfire rang out.The Red Shirts have occupied a 1-square-mile (3-square-kilometer) zone, barricaded by tires and bamboo spikes, in one of the capital's ritziest areas, Rajprasong, since mid-March to push their demands for Prime Minister Abhisit Vejjajiva to resign immediately, dissolve Parliament and call new elections.The Red Shirts, drawn mostly from the rural and urban poor, say Abhisit's coalition government came to power through manipulation of the courts and the backing of the powerful military, and that it symbolizes a national elite indifferent to the poor.