UN chief Ban Ki-moon held landmark talks with Myanmar's President on Monday in a high-profile show of support for changes sweeping through the former pariah state.
During his three-day visit, Ban is expected to urge further steps towards democracy and appeal for unfettered humanitarian access to tens of thousands of refugees who have fled ethnic conflict.
"I would like to extend a warm welcome from the people of Myanmar," said President Thein Sein as the pair met at his official residence in the capital Naypyidaw ahead of an address by the UN leader to the country's parliament.
Ban is also due to meet opposition leader Aung San Suu Kyi on what is his first trip to the country formerly called Burma since decades of military rule ended last year.
It is a far cry from his previous visit in 2009 when the junta dismayed Ban by refusing to allow him to see the Nobel Peace Prize laureate, who was under house arrest at the time.
Suu Kyi has spent much of the past two decades locked up but was freed in 2010 and recently won her first ever seat in parliament in the most visible sign of change under a new quasi-civilian government.
The veteran activist, however, will not be in parliament to hear Ban's address -- the first by a visiting foreign dignitary to the fledgling legislature -- because she and other opposition members are refusing to take their seats in a dispute over the swearing-in oath.
Suu Kyi's National League for Democracy (NLD) has said it will not pledge to "safeguard" an army-created constitution, in the first sign of tension with the government since the April 1 by-elections.
The UN leader is now set to meet Suu Kyi in Yangon on Tuesday.
During his visit to Naypyidaw for talks with President Thein Sein, the UN announced that it would help Myanmar to conduct its first census in 31 years, offering technical support and help mobilising financial support.
Thein Sein, a former army general, has ushered through a broad range of changes since coming to power last year, including welcoming Suu Kyi's party into the political mainstream and freeing political prisoners.
Ban is expected to urge the regime to grant the UN unhindered humanitarian access to tens of thousands of refugees who have fled fighting between the military and ethnic minority rebels in northernmost Kachin state.
Although the UN recently managed to send aid convoys into hard-to-reach parts of Kachin, many refugees remain in dire need of assistance and with the monsoon looming, conditions are expected to become even more desperate.
Ban's visit comes amid a flurry of diplomatic activity to bring the long-isolated state back into the international fold.
The European Union's top diplomat Catherine Ashton is also in Myanmar for talks with Thein Sein following the recent suspension of EU sanctions against the long-isolated country to reward political changes.
Ashton on Saturday met Suu Kyi and opened a new EU office in Yangon that will mostly oversee the management of aid programmes but also have a political role, in a first step towards establishing a full diplomatic mission.