Myanmar security forces have surrounded the headquarters of the ruling Union Solidarity and Development Party (USDP) in the capital, Naypyitaw, and prevented party members in the compound from leaving, party sources in the building said on Thursday.
Several trucks of soldiers and police officers arrived at the compound at around 10 p.m. on Wednesday evening, the sources said. "We have not been allowed to move around since late yesterday," said one party member.
Tension has risen between President Thein Sein and ruling party chief Shwe Mann over the selection of candidates for the general election in November, the party sources said.
Government spokesmen were not available for comment.
The USDP is comprised largely of former military officers and was created from a social movement set up by the former junta.
Both Thein Sein and Shwe Mann have suggested they would accept the job of president after the parliamentary election.
The military, which ruled Myanmar for 49 years maintains an effective veto over the political system and has resisted recent efforts to introduce constitutional amendments to loosen its grip.
The constitution reserves 25 per cent of seats in parliament for unelected military officers. Proposed changes to the constitution require the support of at least 75 per cent of lawmakers, giving the military an effective veto over changes.
A proposed amendment that would have seen the threshold of support lowered to 70 per cent failed, as expected, to gain enough support with lawmakers in a June vote.
Nobel laureate and opposition leader Aung San Suu Kyi has called repeatedly for the military to withdraw from politics.
Her National League for Democracy (NLD) will be the ruling party's main challenger in the election.
Disagreement in the NLD has also emerged over the nomination of candidates for the election.