The incursion on the army's turf was a bold act heavy with symbolism in a country that has experienced 18 successful or attempted military coups since the 1930s.
The most recent was in 2006, when the military ousted Yingluck's brother, former Prime Minister Thaksin Shinawatra, who is living overseas to avoid a corruption conviction but is central to Thailand's political conflict.
Protest organizers later declared that Sunday would be their "victory day," and told followers to seize all state ministries, state telecommunications agencies and other state enterprises, police headquarters and the zoo.
The targets also include the prime minister's offices. In 2008, anti-Thaksin demonstrators occupied those offices for three months to back their demands that his allies step down.
Senior security officials, including the interior minister and the national police chief, went on the government's television station Friday night to ask people not to heed the protest call, calling the proposed actions illegal. Deputy Prime Minister Pracha Promnok said authorities will try to avoid using force in protecting government offices, and accused protest leader Suthep Thaugsuban of causing tremendous damage to the country.
For the past week, thousands of anti-government protesters have marched in Bangkok in a bid to unseat Yingluck, whom they accuse of serving as a proxy for her billionaire brother. Thaksin is adored by much of the country's rural poor and despised by the educated elite and middle class who accuse him of widespread corruption and other offenses.
Leaders of the protests say their goal is not just to force Yingluck out of office but to rid the country of Thaksin's influence in politics.
The demonstrations have raised fears of new political turmoil and instability in Thailand. A planned Bangkok rally on Saturday by Thaksin's supporters has raised tensions further.
Asked if she planned to call early elections, Yingluck told the BBC that she didn't think snap polls would solve the country's problem.
"You have to ask (if) the protesters (would be) satisfied or not," Yingluck said.
Protesters branched out to several spots on Friday, with another crowd staging a rally outside the headquarters of Yingluck's ruling Pheu Thai party, where hundreds of riot police stood guard to prevent them from entering.
A separate crowd of more than 1,000 people marched through central Bangkok to the U.S. Embassy. Opposition lawmaker Korn Chatikavanij, a former finance minister, delivered a letter to an official there denouncing Yingluck's leadership as illegitimate, in response to a statement from Washington that expressed concern about the protests.
Explaining how a crowd of unarmed civilians was able to break through the main gate into the army compound, Gen. Prayuth said: "The army did not want to use any force and we didn't view the protesters as enemies or opponents. They are actually Thais who have different political opinions." But he added, "In any case, security measures will be tightened from now on."
The army compound is next to the United Nations' Asia-Pacific headquarters in Bangkok.
Yingluck has been reluctant to use force against the opposition-led protesters for fear of escalating the crisis and sparking bloodshed.
Security forces have done little to stop protesters who have spent the week seizing government buildings and camping out at several of them in an effort to force a government shutdown while asking civil servants to join their rally.
Crowd sizes peaked Sunday at over 100,000 and have dwindled in recent days to tens of thousands, but organizers have kept each day dramatic by targeting new and different seats of power.
Crowds of protesters have occupied the Finance Ministry since Monday and others have remained holed up since Wednesday at a sprawling government complex that houses the Department of Special Investigation, the country's equivalent of the FBI. On Thursday, the demonstrators cut power at Bangkok's police headquarters and asked police to join their side.
Protest leader Suthep and his allies have called for bigger crowds to join the campaign over the weekend.
Thaksin, who lives in Dubai to avoid serving a jail term for a corruption conviction he says was politically motivated, is a highly polarizing figure in Thailand. Before Thaksin was toppled in a coup for alleged corruption, abuse of power and insulting the nation's revered king he won over Thailand's rural underclass by introducing populist policies designed to benefit the poor. His political movement grew to become the most successful in modern Thai history.
But his opponents saw him as arrogant and a threat to democracy and their own privileges. The country has been gripped by sometimes violent protests by both sides since 2006.
