Barack Obama has begun a tour of South East Asia, which will include a historic visit to Burma.
Mr Obama landed in Thailand's capital Bangkok on his first foreign trip after his re-election as president.
On Monday he will become the first US president to visit Burma, which has been praised in the West for freeing hundreds of political prisoners and holding its first contested election.
contested election：有竞逐的选举
Mr Obama has been trying to refocus US foreign policy towards Asia.
foreign policy：外交政策(diplomatic policy)
Analysts say the US is trying to counterthe dominating influence of China in the region.
But US officials have repeatedly insisted that they want to work with China.
During his Thailand visit Mr Obama will meet Prime Minister Yingluck Shinawatra and King Bhumibol, the world's longest-serving monarch.
In Burma, he is due to hold talks with President Thein Sein and opposition leader Aung San Suu Kyi.
Over the past year the US and other Western nations have relaxed the slew of sanctions they had imposed on Burma, which was ruled by a brutal military regime for five decades.
brutal military regime：残暴的军事政权
But Mr Obama's aides told reporters aboard the president's plane that the US still had concerns about the extent of recent reforms.
Ethnicconflicts remain unresolved, including an increasingly bitter confrontation between Muslim Rohingyas and Buddhist Rakhine people in Rakhine state.
ethnic conflicts：民族冲突
And US officials said they had been seeking assurances that Burma had distanced itself from North Korea, after accusations emerged in 2010 that the two states were sharing nuclear technology.
Some human rights groups have criticised the president for rewarding Burma, even though reforms are nowhere near complete.
Burma has released hundreds of political prisoners but still holds about 300, according to rights groups.
In an amnesty last week some 450 prisoners were freed, but none were on the list of political detainees.
amnesty：特赦
Amnesty International：国际特赦组织(一个有争议的全球监视人组织，监督全球的人权和对联合国和全球的新闻界报告他的结果)
After visiting Burma, Mr Obama will head to Cambodia to join a meeting of the regional bloc Asean.
regional bloc：贸易集团
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