Singapore's Prime Minister Lee Hsien Loong, second from left, signs a charter at the 13th ASEAN Summit in Singapore, 20 Nov 2007

Southeast Asian leaders have adopted a landmark charter that seeks to integrate the region even as a contentious debate about human rights in Burma poisoned the atmosphere of the meeting.

Members of the Association of Southeast Asian Nations (ASEAN) signed the charter at a ceremony Tuesday in Singapore, which gives ASEAN legal identity for international negotiations, and sets out common rules for talks on trade, investment, environment and other fields.

It also calls for the establishment of a human rights agency, but that agency lacks any mechanism for enforcing human rights standards.

The charter still needs to be approved by member countries. The Philippines has warned that its Congress is unlikely to ratify the charter unless Burma's military leaders restore democracy and free detained Nobel laureate Aung San Suu Kyi.

For now, some political analysts note that Burma has succeeded in blocking discussion of its actions.

On Monday, leaders abruptly canceled a briefing by United Nations envoy Ibrahim Gambari, who was to address a regional summit this week about the situation in Burma.

Gambari said he was disappointed about the decision, noting that the reason why he traveled to Singapore was to deliver a briefing on Burma.

Singapore Prime Minister Lee Hsien Loong said late Monday that Burmese Prime Minister Thein Sein strongly objected to Gambari reporting to either the ASEAN summit or the East Asian Summit that follows.

But Lee also read a strongly worded statement from ASEAN leaders calling on Burma to release political detainees and work towards national reconciliation.

The United States has said that ASEAN's handling of military-run Burma has called the group's credibility into question.

ASEAN members are Brunei, Burma, Cambodia, Indonesia, Laos, Malaysia, the Philippines, Singapore, Thailand and Vietnam.

Some information for this report was provided by AFP, AP and Reuters.