Aung San Suu Kyi, the detained Myanmar opposition leader, has said all political prisoners must be freed as a precondition for any visit to the country by the UN secretary general.
A visit by Ban Ki-moon has been mooted as a possible way of breathing life into talks on political reform between the country's opposition and ruling military.
But in a meeting on Monday with Ibrahim Gambari, the UN special envoy to Myanmar, Aung San Suu Kyi was quoted as saying that the release of all political detainees was a "minimum requirement" for any talks to go ahead.
The opposition leader and Nobel peace laureate has herself been held under house arrest for most of the past 19 years.
Monday's talks with Gambari are thought to have been the first contact Aung San Suu Kyi has had with someone from outside Myanmar since she met him in March last year.
Commenting on the meeting, a spokesman for Aung San Suu Kyi's the opposition National League for Democracy said she had explained to Gambari that she was "ready and willing to meet anyone, but she could not accept having meetings without achieving any outcome."
The talks with Gambari took place behind closed doors on Monday morning at a government-owned guesthouse in Yangon, Myanmar's former capital.
Few other details were given of the meeting, which lasted for about an hour.
Gambari's visit is his seventh to Myanmar and comes amid growing frustration at the UN's lack of progress in reconciling the opposition and the military.
|Gambari, left, is on his seventh visit to Myanmar as UN special envoy [EPA]
During Gambari's last visit in August 2008, Aung San Suu Kyi refused to meet him, saying his efforts to bring political reform to Myanmar had shown no sign of movement.
This time however she said she was prepared to hold talks with him if he stepped up pressure on the ruling generals.
On Tuesday, the fourth day of his visit, Gambari is expected to travel to the Myanmar's remote new capital, Naypyidaw, for meetings with senior military officials.
It is not clear however whether he will meet the reclusive ageing leader, Senior General Than Shwe.
UN officials have said that on this visit Gambari wanted to have "meaningful discussions" with all parties, including talks on the country's ailing economy.
Despite rich agricultural land, oil and mineral reserves, Myanmar is one of the poorest countries in Southeast Asia.
The country is still struggling to recover from the impact of Cyclone Nargis last May, which killed an estimated 146,000 people.
After his meeting with Aung San Suu Kyi Gambari was due to travel to the town of Lambutta later on Monday, one of the places hardest-hit by the cyclone.
|Myanmar's military have ruled
the country since 1962 [EPA]
Over the weekend Gambari met government leaders, urging them to release the country's political prisoners and resume dialogue with the opposition.
The military has ruled Myanmar since 1962 and says it is pursuing its own so-called "roadmap to democracy" which will lead to eventual elections for a new national parliament.
Opposition groups have dismissed the roadmap as a sham, because it bars Aung San Suu Kyi and other opposition leaders from public office and guarantees the balance of power remains with the military.
Aung San Suu Kyi led her National League for Democracy to victory in national elections held in 1990, but the military government ignored the results and has kept her under house arrest for most of the intervening years.