The United Nations' special envoy to Myanmar is preparing to make another visit to the country, raising speculation that he may be preparing the groundwork for a visit by the UN secretary general.

Ibrahim Gambari has visited military-ruled Myanmar seven times since his appointment in 2006.

But his visits have so far failed to nudge the country's ruling generals towards significant reform or the release of prominent political prisoners, such as Nobel peace laureate Aung San Suu Kyi.

As Gambari left for Yangon on Wednesday, Ban Ki-moon, the UN secretary general, told the Associated Press he was considering the "appropriate timing" for a visit to Myanmar for face-to-face talks with Myanmar's top general, Than Shwe.

"I'm now evaluating all the possible situations. I have not yet made my decision, but I may have to make [a] decision soon," Ban said.

Myanmar, formerly known as Burma, has been ruled by the military since 1962.

The current regime seized power in 1988 and called national elections in 1990.

But it refused to honour the results of the vote in which Aung San Suu Kyi's National League for Democracy scored a landslide victory.

House arrest

Aung San Suu Kyi herself has been held in jail or under house arrest for most of the past 20 years.

Myanmar has been under military rule since 1962 [GALLO/GETTY]

Yettaw, who is also on trial, and Aung San Suu Kyi, face up to five years in jail if convicted.

Myanmar opposition supporters have condemned the trial as an effort to keep her in detention during elections the government has scheduled for next year as part of what it calls a "road map to democracy".

The vote, expected to take place some time in 2010, has been dismissed by critics as a sham designed to cement the military's continued grip on power behind a veneer of democracy.

Several countries have reportedly urged the UN secretary general to make a personal visit to Myanmar to push for Aung San Suu Kyi's release and to press the government to make next year's election more open and inclusive.

'Important partner'

However, human rights groups and other governments have urged Ban against visiting now, arguing that he could be used by the government.

Ban last visited Myanmar in 2008 and was seen as instrumental in persuading the ruling military to allow more foreign relief workers into the country following the devastation of Cyclone Nargis.

Speaking to the AP about a possible future visit, Ban said he was "concerned about what [the] Myanmar government has done against Daw Aung San Suu Kyi", using a term of respect used in Myanmar.

"I have strongly urged them to drop all the charges against her and release all the political prisoners, including Daw Aung San Suu Kyi."

"She is and can be a very important partner for dialogue for the authorities of Myanmar government. Therefore, whenever I'm ready I'm going to visit and discuss this matter directly in person with Senior General Than Shwe and other leaders."