WASHINGTON (AFP) - The United States voiced confidence on Tuesday that Thailand's military will not stage another coup as worries mount in Washington of fresh turmoil in its oldest Asian ally.

Ms Amy Searight, the top Pentagon official devoted to Southeast Asia, said the United States was "reasonably confident" that the Thai armed forces "will continue to be restrained and professional in all of this."

"At this point we don't have any reason to expect that the Thai military will change their current stance," she told a conference at the Center for Strategic and International Studies in Washington.

Ms Searight said that the Thai military appeared to have learned lessons from 2006, when it overthrew tycoon Thaksin Shinawatra as prime minister and the United States briefly imposed sanctions.

Thailand's judiciary last week removed Prime Minister Yingluck Shinawatra - Thaksin's sister - in the latest twist in the deeply polarised nation's eight years of turmoil that has led to crippling street protests and occasional bloodshed.

Mr Scot Marciel, the top State Department official on South-east Asia, said that Washington was not offering a "US prescription" to resolve the crisis beyond urging a peaceful solution.

"It's important that it be done constitutionally and democratically and, of course, peacefully," Mr Marciel said.

Mr Marciel and Ms Searight both said that US cooperation with Thailand had largely progressed unhindered, with the exception of some work by government ministries closed by street protests.

But both officials declined to predict when Thailand would find a way out of its crisis, which comes as the United States tries to put a greater focus on Asia in the face of China's rise.

Thailand, then known as Siam, in 1833 became the first Asian nation to sign a friendship treaty with the United States. The kingdom famously offered elephants to president Abraham Lincoln to fight the Civil War.