PHNOM PENH, Cambodia (AP) -- Making history twice within hours, President Barack Obama on Monday became the first U.S. president to set foot in Cambodia, a country once known for its Khmer Rouge "killing fields." He left behind flag-waving crowds on the streets of Myanmar, the once internationally shunned nation now showing democratic promise.
Unlike the visit to Myanmar, where Obama seemed to revel in that nation's new hope, the White House has made clear that Obama is only in Cambodia to attend an East Asia Summit and said the visit should not be seen as an endorsement of Prime Minister Hun Sen and the government he has led since the 1980s.
Indeed, Obama's arrival in Cambodia lacked the euphoria of his greeting in Yangon, Myanmar, where tens of thousands of people lined city streets to cheer the first American president to visit a country that had long been isolated from the West. "You gave us hope," Obama declared in Yangon.
In Phnom Penh, the sun was already setting by the time Air Force One landed. Small clusters of Cambodians gathered in the streets to watch the motorcade pass, but there was none of the outpouring that greeted Obama in Myanmar.
Speaking to a national audience from the University of Yangon, Obama offered a "hand of friendship" and a lasting U.S. commitment, yet a warning as well. He said the new civilian government must nurture democracy or watch it, and U.S. support, disappear.
The visit to Myanmar was the centerpiece of a four-day trip to Southeast Asia that began in Bangkok and will end Tuesday in Cambodia, where Obama will visit with Chinese, Japanese and Southeast Asia leaders in addition to attending the East Asia Summit.
Obama celebrated the history of what he was witnessing in Myanmar - a nation shedding years of military rule, and a relationship between two nations changing fast.
"This remarkable journey has just begun," he said.
In a notable detour from U.S. policy, the president referred to the nation as Myanmar in his talks with President Thein Sein. That is the name preferred by the former military regime and the new government, rather than Burma, the old name and the one favored by democracy advocates and the U.S. government.
Deputy national security adviser Ben Rhodes said afterward that Obama's use of Myanmar was "a diplomatic courtesy" that doesn't change the U.S. position that the country is still Burma.
On his first trip abroad since his re-election earlier this month, Obama's motorcade sped him to the lakeside home in Yangon of longtime opposition leader Aung San Suu Kyi. He hugged her and lauded her as a personal inspiration. Suu Kyi spent most of the past 20 years in house detention at her home.
In remarks after their meeting, Suu Kyi echoed Obama's tone with an admonition of her own, one that could have been directed at her own ruling party as much as to the United States:
"The most difficult time in any transition is when we think that success is in sight," she said. "Then we have to be very careful that we're not lured by the mirage of success."
Rhodes said Obama was moved by the opportunity to visit Suu Kyi at her home - and was pleased to see that she had prominently displayed a stuffed replica of the president's dog Bo in the house. Obama gave Suu Kyi the stuffed animal when she visited Washington earlier this year.
Crowds swelled at every intersection, yelling affectionately for Obama and his secretary of state, Hillary Rodham Clinton.
"You are the legend hero of our world," one banner read.
Obama spoke at a university that was once the center of government opposition, and his message was as much a call for Myanmar to continue in its promising steps as it was a tribute to democracy in general. He held up the United States as an example of its triumph and its imperfections.
Coinciding with the president's visit, the government of Myanmar announced further human rights steps to review prisoner cases and de-escalate conflicts in ethnic regions of the country.
But Obama urged even more, calling for a government where, as he put it, "those in power must accept constraints."
"The flickers of progress that we have seen must not be extinguished," Obama said in an address televised to the nation.
Rhodes said the president was moved by the throngs of people who lined the streets to greet him during the visit. The president made one unscheduled stop at the Shwedagon Pagoda. After seeing the pagoda as Air Force One approached Yangon, then seeing the outpouring of support from the citizens for whom the site means so much, Obama personally decided to make the unscheduled stop, Rhodes said.
As Obama arrived in Cambodia, he was dogged by concerns from human rights groups that have cast Hun Sen as a violent authoritarian and have voiced apprehension that Obama's visit will be perceived within Cambodia as validation of the prime minister's regime. But administration officials say Obama, when he meets with Hun Sen on Monday, will raise concerns about the government's human rights record.
Still, many Cambodians credit Hun Sen with helping the country emerge from the horrors of the 1970s Khmer Rouge reign, when systematic genocide left 1.7 million dead. Vietnam invaded and ousted that regime in 1979. By 1985, Hun Sen had become prime minister.