The demonstrators are seeking to topple Yingluck's government, which they believe serves the interests of her brother, former Prime Minister Thaksin Shinawatra, who was ousted by a 2006 military coup after being accused of corruption and abuse of power.
The authorities have exercised extreme restraint over the past week as the protesters besieged and occupied parts of various government ministries and offices, aware that using force could tip public opinion and perhaps become an excuse for the military to take power in the name of restoring order. Conventional wisdom in the Thai capital has been that the protesters have been seeking that.
A special police-led peacekeeping agency said Saturday that the military agreed to send 2,730 personnel to help with security on the streets Sunday. Although the army has declared itself neutral in the current crisis, it deposed Thaksin in 2006 and shows little sympathy for him.
The shootings Saturday night occurred after scattered violence during the day involving government opponents attacking several people they believed were going to a rally at a stadium of "Red Shirt" government supporters.
While the main sites occupied by anti-government protesters remained peaceful, the violence broke out near a stadium where a crowd that appeared to number well over 50,000 Red Shirts rallied in support of the government.
Initially the government foes milled around and jeered the supporters. But then two people were grabbed, one from the back of a motorbike, and beaten. Two buses were attacked, their windows smashed as passengers cowered inside. One protester used an iron rod with a Thai flag wrapped around it to smash the driver's side window of one bus.
The buses and one taxi appeared to have been targeted because they carried people wearing red shirts. Police claimed soon after that they had the situation under control.
But after dark, attacks continued on individual Red Shirts, and the crowds on both sides grew. Many of the attackers were thought to be students from nearby Ramkhamhaeng University.
Police Deputy Spokesman Anucha Romyanan said later on a special television broadcast that fighting broke out between groups of men who threw rocks and other objects at each other and that anti-riot police who were not armed attempted to separate them. An Associated Press journalist at the scene saw no active effort by police on the ground to restore order, though a police helicopter flew overhead.
The dead man was identified as Thaweesak Photkaew, 21, who had two bullets that entered his left ribcage.
In addition to the five other men suffering gunshot wounds, emergency services reported another five people hospitalized with injuries. An AP journalist saw several people at the scene with apparent head injuries.
The week of dramatic protests against Yingluck's government has included seizing the Finance Ministry, turning off power at police headquarters and camping at a sprawling government office complex.
An ill-advised bid by Yingluck's ruling Pheu Thai party to push an amnesty law through Parliament that would have allowed Thaksin's return from exile sparked the latest wave of protests.
Because Yingluck's party has overwhelming electoral support from the country's rural majority, which benefited from Thaksin's populist programs, the protesters want to change the country's political system to a less democratic one where the educated and well-connected would have a greater say than directly elected lawmakers.
Thaksin lives in Dubai to avoid a two-year jail term for a corruption conviction he says was politically motivated.
- AP