"Without the full participation of the democratic opposition and ethnic minority groups, the National Convention lacks the legitimacy necessary to draft a constitution that is truly democratic and representative of the will of the Burmese people," US State Department spokesman Richard Boucher said.
The convention "cannot possibly reflect the true political aspirations of the Burmese people, nor can it conduct the meaningful dialogue that is needed to achieve
The Convention was launched last May but was criticized by Western governments, and the UN has derided it as a sham.
The Committee Representing the People's Parliament, a group representing the democratic opposition, publicly repudiated the Convention for the same reasons on February 12.
The spokesman urged the junta to release Aung San Suu Kyi, National League for Democracy chairman U Tin Oo and the chairman of the Shan National League for Democracy, Hkun Htun Oo, and all political prisoners "immediately and unconditionally."
The junta should allow the NLD to reopen its offices nationwide and to respect fundamental human rights of the people of Myanmar, Boucher said.