Myanmar's high court has rejected an appeal by lawyers representing Aung San Suu Kyi, the detained pro-democracy leader, to reinstate two key defence witnesses in her ongoing trial.

In its ruling on Monday court upheld a previous order barring all but two witnesses from testifying at her trial.

The 64-year-old Nobel peace laureate is charged with violating the terms of her house arrest after an American man swam secretly to her lakeside home and stayed there two days.

She faces up to five years in prison if found guilty.

Her trial is due to resume on July 3 at the Insein prison in Yangon, where court proceedings have been held since May 18.

The court presiding over Aung San Suu Kyi's trial had originally allowed only one of four defence witnesses to take the stand, but a higher divisional court ruled that a second witness could be heard.

According to Nyan Win, one of Aung San Suu Kyi's lawyers, prosecutors had argued that Win Tin, a journalist and former political prisoner, should not be allowed to testify because he is critical of the government and often gave interviews to foreign media.

In response, the defence team said there was no law in the country that bars court testimony from citizens critical of the government.

The prosecution also said that Tin Oo, the deputy leader of the NLD, should not be allowed to testify because he is currently under house arrest.

Envoy's visit

The high court's ruling comes after the United Nations' special envoy to Myanmar wrapped up a two-day visit to the country after meeting senior officials from the military government.

Ibrahim Gambari flew out of the country on Saturday and was expected to brief Ban Ki-moon, the UN secretary-general, before he heads to Asia and possibly to Myanmar.

Gambari met senior Myanmar officials to discuss a possible visit by the UN chief [EPA]

He is thought to have discussed a possible visit by the UN chief, as part of efforts to push Myanmar's military rulers towards political reform.

It was Gambari's eighth visit to Myanmar, none of which have so far been able to nudge the country's ruling generals towards significant reform or the release of prominent political prisoners, including Aung San Suu Kyi.

The opposition leader and head of the National League for Democracy (NLD) has been in detention for more than 13 of the last 19 years.

Her trial has drawn condemnation from world leaders and human rights groups who say Myanmar's military government is using the case to keep her behind bars during elections the government has scheduled for next year.

The military says the vote, expected to take place some time in 2010, is part of what it calls a "roadmap to democracy" for Myanmar.

But the election has been dismissed by critics as a sham designed to cement the military's continued grip on power behind a veneer of democracy.