WASHINGTON -- White House officials cautioned Thursday that President Barack Obama's historic trip to Myanmar, a onetime U.S. adversary, should not be viewed as a "victory celebration."

Obama aides, seeking to assuage critics who say such a visit to the former pariah state is premature, said urgent action was still needed in Myanmar, most notably freeing political prisoners and ending ethnic tension in the western state of Rakhine.

But Danny Russel, Obama's top Asia adviser, said the president's personal appeal to leaders in the nation also known as Burma would be an effective tool in pressing for further democratic reforms.

"This is a moment when we believe the Burmese leaders have put their feet on the right path and that it's critical to us that we not miss the moment to influence them to keep going," Russel said.

Obama will be the first U.S. president to visit Myanmar when he makes a brief stop there Monday. He'll bookend the trip with stops in Thailand and Cambodia, a southeast Asian country with an abysmal record on human rights.

Aides said Obama would raise U.S. concerns about Cambodia's crackdowns on dissidents and civil society groups when he meets with the country's longtime Prime Minister Hun Sen. Cambodia is hosting the East Asia Summit, an annual meeting in which the U.S. participates.

Obama will meet on the sidelines of the summit with outgoing Chinese Premier Wen Jiabao, perhaps their last meeting before the Asian country formerly transfers power for the first time in a decade.

Throughout his first term, Obama emphasized boosting the U.S. presence in Asia, an effort seen as a way to counter China's rising influence.

China's neighbours welcome greater U.S. engagement in the region. But they also want to maintain cordial ties with the region's largest economy, notwithstanding China's assertive behaviour in staking claim to disputed islands in the resource-rich East and South China Seas.

White House officials tamped down the notion of resolving any territorial disputes during Obama's trip.

It's Obama's stop in Myanmar, scheduled to last about six hours, that is the centerpiece of his first foreign tour since winning re-election.

The U.S. has ended diplomatic isolation of Myanmar and suspended tough economic sanctions as the country has shifted from five decades of oppressive military rule. Its government has reconciled with its famed opposition leader Aung San Suu Kyi, a former political prisoner who is now a lawmaker.

Obama will meet with both Suu Kyi and Myanmar's President Thein Sein. But he is not expected to take the symbolic step of referring to the country as Myanmar, the name bestowed on it by its former military rulers.

Tom Donilon, Obama's national security adviser, said the burgeoning relationship between the U.S. and Myanmar could demonstrate to nations like North Korea the benefits of opening up to the world.

"That is a path that if North Korea would address the nuclear issue would be available to them. We have said that from the outset. It's an important example for them to contemplate," Donilon told an audience at the Center for Strategic and International Studies in Washington.

But he said the U.S. sees no sign that rulers in Pyongyang, the North Korean capital, have decided to go the same way. He said it needs to demonstrate serious intent on ending its nuclear weapons program.

North Korea has conducted two nuclear tests, and recent commercial satellite imagery suggests it has continued to develop long-range ballistic missiles since it attempted to launch a rocket into space in April in defiance of a U.N. ban. That launch sank an Obama administration effort to give the impoverished country food aid in exchange for nuclear concessions.