About 1,500 anti-government protesters forced their way into the compound of Thailand's army headquarters on Friday, the latest escalation in a demonstration seeking to topple Prime Minister Yingluck Shinawatra.

"We want to know which side the army stands on," shouted one protester, as others scrambled over the compound's red iron gates in Bangkok's historic quarter. In another district, about 1,000 gathered outside the prime minister's ruling party headquarters, shouting "Get out, get out".

The invasion of the headquarters deepens a conflict broadly pitting the urban middle class against the mostly rural supporters of Yingluck and her brother Thaksin Shinawatra, a former prime minister who was ousted in a 2006 coup and who remains central to Thailand's eight years of on-off turmoil.

The protesters accuse Yingluck of abusing her party's parliamentary majority to push through laws that strengthen the behind-the-scenes power of her self-exiled, billionaire brother. They have rejected her repeated calls for dialogue.

Although the army moved its main command center to a military camp in Bangkok's suburbs three days ago, the siege of its grounds by protesters is deeply symbolic and highlights the military's pivotal role in a country that has seen 18 successful or attempted coups in the past 80 years.

After forcing open the compound's wrought-iron front gates, protesters swarmed inside, demanding that generals choose sides. About 100 soldiers stood guard. Hundreds watched from the balconies of the 19th-century cream-colored building.

"We want the head of Thailand's armed forces to choose whether they stand by the government or with the people," Uthai Yodmanee, a protest leader, said from the back of a truck.

Crowds of protesters have occupied the Finance Ministry since Monday and others remain holed up at a sprawling government complex that houses the Department of Special Investigations, the country's equivalent to the FBI. On Thursday, the demonstrators cut power at Bangkok's police headquarters and asked police to join their side.

Yingluck has publicly courted Thailand's powerful military, which has remained neutral in this bout of protests.

'Above the law'

"The army wishes all sides to solve the problem with the country's best interests in mind," said deputy army spokesman Colonel Winthai Suvaree.

Compare that to 2008, when Thailand was convulsed by protests that helped topple two Thaksin-allied governments.

In October 2008, after bloody clashes between police and demonstrators rallying against then-prime minister Somchai Wongsawat, Thaksin's brother-in-law, the military took sides. Then army chief Anupong Paochinda urged Somchai to step down to take responsibility for the violence.

Memories of that help explain why Yingluck appears to have studiously avoided a confrontation during six days of protests against her government. Police have remained restrained, separated by gates and razor wire from protesters who at times pelt them with water bottles and shout insults.

The protest leader, Suthep Thaugsuban, a deputy prime minister in the previous government, told thousands of supporters late on Thursday that "the end game will happen in the next day or two".

Democrat leader Abhisit Vejjajiva, former prime minister of a military-backed government that Yingluck routed in a 2011 election, joined the protests on Friday along with other Democrats including former finance minister Korn Chatikavanij.

"When the government acts above the law, the people no longer need to respect the government," Korn told a crowd of thousands in Bangkok's Asoke commercial district.

Reuters-AP