Burma's military rulers are pressing ahead with plans to call a constitutional convention Monday, despite a boycott by the country's two largest pro-democracy parties.

Military officials say they will convene the meeting "in the interests of national unity" and insist a new constitution will be Burma's first step in the "road map to democracy."

However, foreign diplomats in Rangoon say the process has lost its credibility before it started, because of a boycott by Burma's major opposition groups.

The main opposition party, the National League for Democracy, said Friday it will not take part because military rulers have not released its leader, Aung San Suu Kyi from house arrest. The party said the government also has ignored other key conditions that would have allowed members of the opposition to participate in drafting a new national charter.

The NLD was joined Saturday by Burma's second largest pro-democracy party, the Shan Nationalities League for Democracy, which also said it will not attend. Other small ethnic pro-democracy parties made similar announcements.

U.S. officials have urged Burma to take into account the views of opposition groups. In a statement, the U.S. State Department said national reconciliation and democracy in Burma depend on discussions between the government, ethnic minorities, and the NLD.

At the United Nations Friday, Secretary-General Kofi Annan urged Burma's government and the opposition to reach a compromise that would allow Aung San Suu Kyi to participate in the meeting.

In Washington, U.S. Senator John McCain said Burma must free Aung San Suu Kyi and NLD deputy leader Tin Oo, if it is serious about moving toward democracy. Mr. McCain said he supports the NLD's decision to boycott the convention, which he said was only organized to ease international pressure on Burma.

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