Ojea was scheduled to meet Friday with diplomats based in Yangon and the legal team of opposition leader Aung San Suu Kyi, who is serving an 18-month house arrest sentence, UN sources said.

The junta has so far agreed to a meeting between Quintana and four lawyers from Suu Kyi's National League for Democracy, according to an official and NLD party spokesman, also called Nyan Win.

Ojea said in Geneva that he hoped to meet with Suu Kyi and other political leaders during his third mission to Myanmar, which is scheduled to hold a general election some time this year.

"It would be important for me to meet with political party leaders in the context of this year's landmark elections," he said in Geneva.

There are at least 2,100 political prisoners in jail in Myanmar, deemed a pariah state among Western democracies.

Suu Kyi, 65, leader of the National League for Democracy (NLD) opposition party, has spent 14 of the past 20 years under detention.

On Saturday, Myanmar authorities released Tin Oo, the 84-year-old deputy leader of the NLD, after keeping him under house detention for seven years.

Tin Oo was a founder of the NLD. The party won the 1990 general election but was denied power by Myanmar's ruling military regime.

The junta has promised to stage an election this year, although many analysts doubt it would be free or fair. The 2008 constitution pushed through by the military assures the army a controlling role over any elected government, by allowing it to dominate the Senate.

It is not yet clear whether the NLD will contest the election.

Authorities arrested Tin Oo in May 2003 on charges of disturbing public order, after pro-government militias attacked the convoy carrying him and Suu Kyi near Depayin, in Upper Myanmar.

In August, a Yangon court sentenced Suu Kyi to 18 more months under house arrest for breaking the conditions of her previous detention, by allegedly allowing US citizen John Yettaw to swim to her lakeside compound.

Quintana expects to meet Foreign Minister Nyan Win but not reclusive junta head Than Shwe during his trip.

Quintana has said he also wants to meet Suu Kyi but the ruling generals have not said if they will allow the Argentine diplomat to do so.

He arrived by commercial flight at Yangon airport and was taken to his hotel before meeting with UN staff, a Myanmar official said on condition of anonymity.

In a statement issued last week ahead of his visit, Quintana said 2010 was "a critical time for the people of Myanmar." "It would be important for me to meet with political party leaders in the context of this year's landmark elections," he said.

"I hope that my request to the government to meet with... Aung San Suu Kyi will be granted this time."

Quintana had meant to visit Myanmar back in November but his visit was repeatedly pushed back. He was appointed to his human rights role in May 2008 in the wake of a cyclone that left around 138,000 people dead.

On Thursday the envoy is due to return to Yangon to visit the country's notorious Insein prison where dozens of political dissidents are held, and later meet with representatives of ethnic groups.

Some ethnic groups along Myanmar's eastern border continue to wage armed opposition to the government.

Quintana will go to the remote capital Naypyidaw to meet with senior government officials on Friday before leaving the country.

His trip comes as the junta sends out mixed signals to the international community, by responding to US efforts at engagement while at the same time continuing a crackdown on dissent ahead of this year's promised polls.

The junta has in the recent past exercised strict controls on all UN officials visiting the country, including Secretary-General Ban Ki-moon last year, who was refused access to Suu Kyi.

US officials have by contrast received a warm welcome since President Barack Obama's administration announced that it would pursue a dual track of engagement alongside sanctions.