Alleging fraud, the military regards the November general election won by the then ruling National League for Democracy party in a landslide as void, and promised to hold a "free and fair" election, with power handed over to the winning party.

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During a meeting at a government guesthouse compound in the capital Naypyitaw, however, the NLD members declared the opening of a parliament of their own and signed an oath of office.

One of the participants, speaking to local media, claimed the legitimacy of the assembly, saying, "We have been elected by the people."

The military took over power on Monday hours before parliament was scheduled to convene for the first time since the Nov. 8 election. By law, a new regular session of parliament must be held within 90 days of a general election.

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The NLD won 396 of 476 seats contested in the last general election, securing a comfortable majority in the 664-seat bicameral parliament. In contrast, the military-backed main opposition party secured just 33 seats.

Earlier Thursday, a senior NLD official said by phone that most of the party's top executives were still being detained by the military following the coup.

With around 15 Central Executive Committee members including Suu Kyi and ousted President Win Myint detained, Aung Kyi Nyunt, who himself is a committee member, said the risk of the party being forcibly dissolved has become higher as the military continues to search and close NLD offices across the country.

He said that such actions amount to blocking the democratic system as a whole in the country, thus making it a matter of international concern.

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The military, which declared a one-year state of emergency in seizing power and ending a decade of civilian rule in the country, is believed to be holding Suu Kyi and the NLD members in the capital.

Also Thursday, the U.N. Security Council expressed "deep concern" at the declaration of the state of emergency in Myanmar and called for "the immediate release of all those detained," including Suu Kyi and Win Myint.

The council statement, issued with the consent of all 15 member countries, however, stopped short of referring to the military takeover as "coup." Nor did it condemn the move.