Thein Sein was due to attend a summit for leaders from the 10-nation Association of Southeast Asian Nations (ASEAN) bloc hosted by US president Barack Obama, who has staked large political capital in Myanmar's passage towards greater democracy.

Suu Kyi and hundreds of newly-elected MPs from her National League for Democracy party (NLD) took their seats in parliament two weeks ago after dominating the country's fairest poll in decades in November.

But what observers said was a surprisingly smooth initial phase of the political transition has since been clouded by rumours and speculation - especially over who will be tipped to succeed Thein Sein as President.

The wildly popular democracy icon Suu Kyi is barred from the post by a charter penned by the military that kept her under house arrest for 15 years during repressive junta rule.

The constitution also reserves a quarter of parliamentary seats for appointed military officers, handing the army an effective veto on charter change.
 With the NLD-dominated parliament putting off presidential nominations until late March, rumours have swirled that the party is engaged in back-room talks in a bid to amend the charter and pave the way for a Suu Kyi Presidency.

The delicacy of the transition was underscored by Thein Sein's last-minute decision to cancel the California trip, seen as his final chance to cement a legacy on the  global stage as the reformist leader who guided Myanmar out of five decades of cloistered military junta rule.

Myanmar's Vice President Nyan Tun will  now attend the February 15-16 summit at the Sunnylands estate in California, the president's office said.

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