Yangon  - A Myanmar court on Friday rejected an appeal lodged by opposition leader Aung San Suu Kyi against an 18-month detention sentence, government sources said.

Suu Kyi's lawyers had opened the appeal case at the Yangon Divisional Court in a bid to overturn a court verdict in August that found Suu Kyi guilty and placed her under house detention for another 18 months.

Nyan Win, one of Suu Kyi's lawyers, has promised to appeal the case up to the Supreme Court level.

On August 11, a special court set up in Yangon's Insein Prison found Suu Kyi, 64, guilty of violating the terms of her house arrest and sentenced her to three years in prison with labour. The sentence was quickly commuted to 18 months under house detention by Myanmar's military supremo, Senior General Than Shwe.

Suu Kyi, who has spent 14 of the past 20 years under detention, was found guilty of allowing US national John William Yettaw to swim to her lakeside home-cum-prison on May 3, where he stayed uninvited until May 5. Yettaw claimed he carried out the stunt to warn her of an assassination attempt he had envisioned.

Suu Kyi's two household aides, Khin Khin Win and Win Ma Ma, were also found guilty of abetting Yettaw's visit and were sentenced to three years in jail, which was also commuted to 18 months under house arrest. Their cases have also been appealed by Suu Kyi's legal team.

The Nobel Peace Prize winner's lawyers have appealed the verdicts on the grounds that Suu Kyi was detained on charges of threatening national security based on the 1974 constitution, which has been replaced by the 2008 charter. There is no similar reference to national security in last year's charter.

Yettaw's swimming escapade provided a pretext for Myanmar's military regime to accuse Suu Kyi of violating the terms of her detention and to keep her out of the political picture for the next 18 months while it prepares for a general election next year, which promises to be neither free nor fair.

Yettaw, 54, was sentenced to seven years in prison but was freed August 16 at the request of visiting US Senator Jim Webb, chairman of the US Senate's East Asia and Pacific Affairs Subcommittee.

Webb, in a rare interview with Than Shwe, also requested that Suu Kyi be released but failed to secure her freedom.

Suu Kyi's ongoing house detention meant that it was unlikely that her National League for Democracy opposition party, which won the last polls in 1990 but has been denied power for the past 19 years, would participate in next year's election.

It also dashed hopes that prior to the polls, the regime might open a dialogue with the democracy icon and consider amending the 2008 constitution, which essentially cements the military's control over any democratically elected government.

Myanmar has been under military rule since 1962. (dpa)