Burma's Supreme Court on Friday rejected an appeal by Aung San Suu Kyi against her extended house arrest, her lawyer said, keeping her in detention ahead of elections promised by the junta this year.

The opposition leader, who has spent most of the last two decades locked up, had her incarceration lengthened by 18 months in August after being convicted over a bizarre incident in which a US man swam to her lakeside home.

Her legal team immediately vowed to lodge a final "special" appeal with Burma's chief justice to win her freedom. Suu Kyi was not at the court in the former capital Yangon to hear Friday's verdict.

burma aung san suu kyi "The appeal was rejected. They just read out the order which did not include the reason, so we do not know why they rejected it," said Nyan Win, her lawyer and the spokesman for her National League for Democracy (NLD).

Nyan Win said he was neither surprised nor disappointed by the ruling against Suu Kyi.

"Today we will go for a special appeal," he said.

The next step would be to write to the chief justice and ask for a panel of judges in Yangon to hear the special appeal, he said. If that failed they could ask for a similar appeal to be heard in the new capital Naypyidaw.

A lower court threw out an initial appeal against her house arrest in October.

A Burma official said the court had also rejected appeals by Suu Kyi's two female live-in assistants against similar periods of detention.

Suu Kyi has been in jail or under house arrest for 14 of the last 20 years since the country's last elections in 1990, which the NLD won by a landslide. The junta then prevented the party from taking power.

She has previously dismissed comments by Home Affairs Minister Maung Oo, who reportedly said she would be released in November, as "unfair" ahead of any court decision.

Junta chief Than Shwe has promised to hold elections this year under his "roadmap to democracy" but has failed to set a date. Critics say the polls are aimed at simply entrenching the generals' power.

Foreign ambassadors including the British, French and Australian envoys went to the court for Friday's verdict.

No surprise

French ambassador Jean-Pierre Lafosse said the ruling "came as no surprise to us," adding: "She should be released immediately as one of the conditions for real national reconciliation."

Suu Kyi's continued detention keeps her off the scene for the elections, in which she is effectively barred from standing anyway by the constitution. A quarter of the parliamentary seats up for grabs are also reserved for the army.

She has said it is too early for her party to decide whether to participate.

Exiled Burma activist Aung Din of the US Campaign for Burma said the international community had to put more pressure on the regime.

"I am not surprised by the Supreme Court’s decision. Than Shwe already made the verdict for Daw Aung San Suu Kyi and no judge will have the nerve to change it," he said.

At least 2,100 other political prisoners remain behind bars in Burma, according to UN figures.

Friday's ruling comes a week after UN human rights envoy Tomas Ojea Quintana visited the country, saying as he left that he "deeply regretted" being refused access to Suu Kyi during his five-day trip.

Burma's government has given out mixed signals ahead of the polls, in mid-February releasing deputy NLD leader Tin Oo after seven years of detention, but jailing five other dissidents during Quintana's visit.

Suu Kyi herself has made efforts to defrost relations with the junta, writing twice to Than Shwe since September to offer help in getting Western economic sanctions lifted and asking to meet with him.

The thaw came as US President Barack Obama's administration pursued greater engagement with the Burma regime after deciding that sanctions alone were not working.

- AFP