Aung Sun Su Kyi, Now, What are you Doing?

The international community greeted her election as a step towards democracy and had urged Suu Kyi, who drew huge crowds on the campaign trail, to take her seat amid fears her refusal could stall the transition from military rule.

Hilary Clinton and Daw Su

US Secretary of State Hilary Clinton, on a visit to Beijing Wednesday, praised Myanmar's president for allowing the by-elections but said the United States was also looking ahead to the conduct of polls slated for 2015.

"This is an important moment for Myanmar's future," Clinton said in a statement, using Myanmar's former name.

"A genuine transition toward multi-party democracy leading to general elections in 2015 will help build a more prosperous society."

The NLD is the main opposition force after securing 43 of the 44 seats it contested in the by-elections. The party, which boycotted a controversial 2010 election, agreed to rejoin the political mainstream last year after a series of reforms by the government.

But it is still a minority influence in parliament with one quarter of the seats in both chambers reserved for unelected military officials.

Renaud Egreteau, a Myanmar expert from the University of Hong Kong, said Suu Kyi's retreat over the oath showed that compromise was now among her "political tools".

While taking office had opened new political ground, Egreteau cautioned Suu Kyi and the NLD against participating "in the army's constitutional game while refusing the rules."

Ban Ki-moon and Daw Su

Appearing alongside UN chief Ban Ki-moon, who arrived for talks at her lakeside villa in Yangon on Tuesday, Suu Kyi said she was willing to compromise for the sake of reform.

"We have always believed in flexibility, in the political process... that is the only way in which we can achieve our goal without violence," she said.

The democracy icon, who was released from house arrest in 2010, has shown increased confidence in the government in recent weeks, calling for the suspension of EU sanctions and planning her first international trip in 24 years.

Last week, European Union nations suspended most sanctions against the resource-rich but poor nation for one year to reward the reforms, which included releasing some political prisoners.

But the United States has ruled out an immediate end to its main sanctions.

Suu Kyi's long journey from political prisoner to politician has come at great personal cost.