Naypyidaw:  Myanmar's Parliament reopened with Aung San Suu Kyi refusing to take a seat on Monday, while the nation's President vowed "no U-turn" on reforms as the EU prepares to suspend sanctions.

READ MORE: EU to suspend sanctions against Myanmar

Suu Kyi's party has refused to swear to "safeguard" an Army-created constitution in the first sign of tension with the government since a landmark by-election this month saw the democracy icon win a parliamentary seat.

The spat comes as European Union nations are preparing to suspend most sanctions against the impoverished nation for one year to reward a series of dramatic reforms since direct army rule ended last year.

Myanmar, long-isolated under military dictatorship, has seen a rapid improvement in relations with the international community after the Nobel Peace Prize winner and her party achieved a decisive win in the April 1 polls.

Suu Kyi has shown increased confidence in the reformist government of President Thein Sein in recent weeks, calling for the EU sanctions suspension and planning her first international trip in 24 years.

Thein Sein, who is currently on a visit to Japan, on Monday vowed that he would not backtrack on the country's democratisation.

"There won't be any U-turn," Thein Sein said, according to the Mainichi Shimbun. But he rejected the suggestion that he would alter Myanmar's parliamentary oath to accommodate Suu Kyi, telling reporters that it was up to her whether or not she took the seat.