Barack Obama will arrive in Bangkok on Sunday, the first leg of a three country tour that will include bilateral talks with Thai prime minister Yingluck Shinawatra and the first visit by a sitting US president to Myanmar.
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The regional visit by Mr Obama, en route to the East Asia Summit in Cambodia, will cap an unusual flurry of high-level US diplomatic activity in southeast Asia with Hillary Clinton, secretary of state, landing in Thailand on the same day.
The visits, along with that of Leon Panetta, the US defence secretary, on Thursday, are aimed at "deepening ties" with Thailand and its neighbours, say US officials. The moves are part of a strategy the US describes as "rebalancing" or shifting strategic focus and military influence towards Asia.
During talks in Bangkok Mr Panetta agreed to upgrade the US-Thai defence alliance. The agreement includes initiatives to allow Thai and US military forces to work more closely and extend collaboration on regional and multilateral security efforts. As part of this co-operation the US and Thailand will invite neighbouring Myanmar to observe the next joint exercises in Thailand in early 2013.
Myanmar's inclusion in the largest multilateral land military exercises, even while the US maintains sanctions that prohibit arms sales, reinforces US eagerness to deepen regional security relations.
Both the US and Thailand have denied that such measures and the upgrading of bilateral security ties are aimed at offsetting China's growing regional presence.
Privately, however, both US and southeast Asian officials have voiced concerns about China's territorial claims in regional waters and the deterioration of Beijing's relationship with Japan.
Recent US efforts to re-engage with Myanmar's military – which developed close security as well as economic ties with China over decades of diplomatic isolation by the west – reflect the new priorities.
Thitinan Pongsudhirak, professor of international relations at the Bangkok-based Chulalongkorn University, noted an increasing divergence in attitudes among maritime and mainland southeast Asia towards China and the US. "If China can step back on [its] South China sea claims and the US can reassure Beijing of its benign rebalance, both maritime and mainland southeast Asia would have more in common under the regional umbrella," he noted.
At a briefing at US think-tank CSIS on Thursday, Tom Donilon, the US national security adviser, said the US was pursuing "a stable and constructive relationship with China". There were "elements of both co-operation and competition", he noted, "but getting the US-China relationship right is a long-term effort. We will continue to make this a priority in President Obama's second term and as China's new leadership takes the reins."
The US rebalancing towards Asia-Pacific was also a "long-term undertaking", he said, noting: "The president will make clear once again over coming days, the region will continue to be a foreign policy priority for years to come."
Mr Obama's lightning half-day visit to Myanmar on Monday will be the first by a sitting US president to the country, just months after the US eased economic sanctions and barely 18 months after the accession of President Thein Sein, who launched unprecedented reforms.
However, in a diplomatic backhander, Mr Obama will confine his five-hour visit to Yangon, avoiding the capital, Naypyidaw, in a move that will force Mr Thein Sein to journey 320km south to meet his US counterpart.
Diplomats say the decision was in response to concerns expressed by Aung San Suu Kyi. The opposition leader echoed the warnings of some human rights groups that it was too soon to reward Myanmar's leaders with a US presidential visit. Although Washington recognises Naypyidaw as Myanmar's capital, Mr Obama wanted to avoid any implicit endorsement of the former military regime of Than Shwe, which abruptly moved the capital in the early 2000s.