The request by Ban Ki-moon to meet with jailed Burmese opposition leader Aung San Suu Kyi has been rejected during what the UN secretary general has called a "very tough" diplomatic mission.

Ban met with junta chief Than Shwe, the senior general in Naypyidaw, the administrative centre of Burma, also known as Myanmar, on Friday and requested a meeting with Suu Kyi face-to-face.

Ban said he was told the request was denied because Suu Kyi is still on trial. He said he repeated his request, stressing its importance, and is waiting for another reply.

Suu Kyi, 63, has been jailed for nearly 14 of the last 20 years. The pro-democracy leader is on trial for allegedly breaking the terms of her house arrest in May by letting American John Yettaw stay in her lakeside Rangoon home for two days.

If convicted, Suu Kyi faces five years in jail. Burmese officials announced Friday, after Ban arrived in the country, that her trial, which had been set to resume, has been adjourned until July 10, when the defence's final witness will take the stand.

Ban has said one of the key goals of his visit to Burma is to garner the release of all political prisoners, including Suu Kyi.

Ban is the first UN secretary general to meet with the Nobel Peace Prize laureate since her first period of detention started in 1989.

The UN chief said he also wants to encourage the junta to resume dialogue with the opposition and to ensure conditions exist for credible elections in 2010.

"I would like to help move your country forward and appreciate your commitment to moving your country forward," Ban told Than Shwe ahead of their one-hour meeting.

Ban is also scheduled to meet Prime Minister Gen. Thein Sein before meeting with ethnic minority groups and leaders of opposition political parties, including Suu Kyi's National League for Democracy.

Refuse to relinquish power

Suu Kyi's opposition party won national elections in 1990, but Burma's generals refused to relinquish power.

Her trial has sparked international outrage from world leaders, including accusations that the ruling junta is trying to keep Suu Kyi in detention during elections it has planned for next year.

Ban said that he was "assured that the Myanmar authorities will make sure that this election will be held in a fair and free and transparent manner."

Senior UN officials travelling with Ban called the trip a "highly risky" one for the secretary general, whose image would suffer if the junta ignores his demands — as it has repeatedly shunned global calls in the past for democratic reforms.

"This is going to be, I know, a very difficult mission," Ban told reporters while en route to Burma. "But at the same time, I know that to bring changes to Myanmar, political conciliation and democratization, we need to do our best."