BANGKOK (Reuters) - President Barack Obama kicked off a three-country Asia tour with a visit to Thailand on Sunday, using his first post-election trek overseas to try to show he is serious about shifting the U.S. strategic focus eastwards.

Obama's itinerary will include a landmark visit to once-isolated Myanmar and an East Asia summit in Cambodia as he seeks to recalibrate U.S. economic and security commitments to counter China's influence at a time when America is disentangling itself from wars in Iraq and Afghanistan.

But his attention will be divided during his travels as he faces a simmering crisis in the Gaza Strip pitting Israel against Hamas militants and also contends with a looming fiscal crisis at home.

Flying into Bangkok, Obama was due to tour the iconic Wat Pho Royal Monastery and have a royal audience with King Bhumibol Adulyadej at the hospital where he has been recovering from an illness since September 2009. He will also hold talks and a joint news conference with Prime Minister Yingluck Shinawatra.

The U.S. administration regards Thailand as a key ally for advancing an "Asia pivot" that Obama announced last year with an eye to an increasingly assertive China. Obama, who was born in Hawaii and spent part of his youth in Indonesia, has called himself America's first "Pacific president."

His choice of Southeast Asia for his first foreign trip since winning re-election on Nov. 6 is meant to show he intends to make good on his pledge to boost ties with one of the world's fastest-growing regions, a strategy his aides see as crucial to his presidential legacy. It is his second extensive trek through Asia in little more than a year.

In the centerpiece of his three-day tour, Obama on Monday will make the first U.S. presidential visit to Myanmar, also known as Burma, marking a new milestone in Washington's rapprochement with the former pariah state where a fragile transition is under way after decades of military rule.

Some international human rights groups object to the visit, saying Obama is rewarding the country's quasi-civilian government before democratic reforms are complete.

Obama aides said the Myanmar trip is meant to lock in progress so far and that he will speak forcefully on the need to do more on human rights, especially to curb sectarian violence.

He will meet President Thein Sein and famed opposition leader Aung San Suu Kyi, who - like Obama - is a Nobel Peace Prize laureate.