Thai protesters briefly stormed the army's headquarters in Bangkok on Friday and called on the military to help oust Prime Minister Yingluck Shinawatra, just as it had toppled her brother in a 2006 coup.
Meanwhile, another group of protesters marched to the U.S. Embassy, where they delivered a letter denouncing Ms. Yingluck's government as illegitimate.
Ms. Yingluck's brother, Thaksin Shinawatra, is a former prime minister and billionaire telecommunications tycoon. He lives in exile in Dubai to avoid a two-year prison sentence for a conviction on corruption charges, which he says are politically motivated.
In an interview with the British Broadcasting Corp. Ms. Yingluck, who has been prime minister since 2011, ruled out early elections, saying that would not calm the protesters.
"I love this country. I devote myself to this country. I need only one thing for the country: we need to protect democracy," she said.
Protest leaders have rejected her proposals for talks, and she has rejected the use of force against the protesters.
The army ousted Thaksin in 2006 following allegations of corruption and abuse of power. But it has refused to take sides in the current crisis, which has fomented in recent months.
"Don't try to make the army take sides because the army considers that all of us are fellow Thais, so the government, state authorities and people from every sector must jointly seek a peaceful solution as soon as possible," army commander Gen. Prayuth Chan-ocha said in a statement reported by The Associated Press.
The protesters accuse Ms. Yingluck of acting as a proxy for her brother, and say they will escalate their efforts on Sunday.
The anti-government protests are the largest in three years in the Southeast Asian nation.
The Obama administration earlier this week expressed concern about political tensions in Thailand.
"We urge all sides to refrain from violence, exercise restraint, and respect the rule of law," said State Department spokeswoman Jen Psaki. "Violence and the seizure of public or private property are not acceptable means of resolving political differences."
"The United States firmly believes all parties should work together to resolve differences through peaceful dialogue in ways that strengthen democracy and rule of law," she added.
Thaksin and his allies have won every national election since 2001.
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