Southeast Asian leaders will meet for an annual summit set to be dominated by Burma's historic reforms, North Korea's planned rocket launch and strategic maritime disputes with China.
Leaders of the 10-member Association of Southeast Asians (ASEAN) gather in the Cambodian capital two days after by-elections in Burma saw opposition leader Aung San Suu Kyi win her first seat in parliament.
Election monitors from Cambodia, which holds the ASEAN chair, have declared Sunday's vote free and fair, and urged the international community to lift sanctions imposed over the Burma military's long record of rights abuses.
ASEAN foreign ministers applauded the "orderly" conduct of the polls during talks in Phnom Penh on Monday, setting the stage for a strong endorsement from the bloc's leaders at the conclusion of the two-day summit.
Surin Pitsuwan, ASEAN's secretary-general, said the vote should contribute to the "reintegration of Myanmar into the global community", a reference to the possible lifting of Western sanctions.
Indonesian Foreign Minister Marty Natalegawa welcomed the by-elections as "an opportunity for Myanmar to make the reform process even more irreversible".
Philippine Foreign Secretary Albert del Rosario said they were a "vindication of the global community that believed that Myanmar could pursue this democratisation track effectively".
Burma's poor human rights record and iron-fisted suppression of political dissent have often hijacked ASEAN gatherings in the past, much to the embarrassment of more democratic member-states.
But over the past 12 months the country's quasi-civilian government, led by President Thein Sein, has freed hundreds of political prisoners, eased media restrictions and welcomed the opposition back to the political fold.
At the last ASEAN summit in November, the country was rewarded for its efforts by being promised the bloc's chairmanship in 2014. Myanmar is eager too to win greater foreign investment with the prospect of sanctions being lifted.
ASEAN comprises Brunei, Cambodia, Indonesia, Laos, Malaysia, Burma, the Philippines, Singapore, Thailand and Vietnam -- a grouping of nearly 600 million people from disparate economic and political systems.
North Korea's planned rocket launch -- described by Pyongyang as a bid to send a satellite into orbit but condemned by the United States and its allies as a thinly disguised missile test -- is also looming over the summit.
Del Rosario said the ASEAN foreign ministers spoke with one voice against the nuclear-armed North's launch plans.
The Philippines -- which lies beneath the rocket's proposed flight path -- has lodged formal protests with Pyongyang's representatives at the United Nations, in China and at ASEAN.
"I think the countries that spoke on the topic... were all of the opinion that we should be discouraging (North Korea) from undertaking that launch," Del Rosario said after the foreign ministers' meeting on Monday.
Regional tensions with China over disputed islands in the South China Sea are another vexing issue for the ASEAN leaders, diplomats said.
China has competing territorial claims in the sea with ASEAN members the Philippines, Vietnam, Malaysia and Brunei. The United States says it has a "national interest" in keeping the vital trade route open to shipping.
The sea is a conduit for more than one-third of the world's maritime trade and half its traffic in oil and gas, and major petroleum deposits are believed to lie below the seabed.
US ally the Philippines has been leading a push for ASEAN to first form a united front before meeting with China and getting it to agree on a "code of conduct" in the sea, but other members argue that Beijing should be involved from the start.
