Myanmar's parliament speaker said Tuesday the current junta-drafted constitution, which bars opposition leader Aung San Suu Kyi from becoming president, cannot be changed before elections in November 2015.

The comments by Shwe Mann came days after visiting US President Barack Obama backed Suu Kyi's attempts to change the charter.

The speaker said a nationwide referendum would be held next May on constitutional changes which are currently being thrashed out amid heated debate in the legislature.

"We cannot perform constitutional amendments straight after the referendum," Shwe Mann told reporters in the capital Naypyidaw, adding it was "impossible to change (the charter) at this time" because of the scope of the likely changes.

On Monday the powerful military voiced strong opposition to significant changes to the constitution, including clause 59f which is widely thought to have been written specifically to thwart Suu Kyi.

Legislators will choose a new president after the general election next November.

But the veteran democracy campaigner cannot stand for the top post because the constitution bans those with a foreign spouse or children.

Her late husband and two sons are British.

- 'Unfair, unjust and undemocratic' -

Next year's elections are seen as a crucial test of the credibility of reforms begun in 2011, when the junta stepped aside to make way for a quasi-civilian regime that remains dominated by former generals.

Suu Kyi and her National League for Democracy (NLD) party are expected to make big gains at the polls -- the first general election they have fought since they swept 1990 polls. The then-junta ignored the result.

But the party has so far declined to put forward an alternative candidate if Suu Kyi, 69, cannot stand for the presidency.

NLD MP Min Thu told AFP the party still "has hope" that Suu Kyi will be able to become president after the election.

"If people want it enough, everything will come true. Nothing can be done without the people's desire," he said.

The Nobel laureate, who has publicly declared her desire to be president, last week told Obama the constitution was "unfair, unjust and undemocratic" and warned that Myanmar's much vaunted reforms were stalling.

The US leader took up the issue, telling reporters at her lakeside home that "the amendment process needs to reflect inclusion rather than exclusion".

"I don't understand the provision that would bar somebody from running for president because of who his (someone's) children are," he added.

- Army veto -

Unelected soldiers currently make up a quarter of Myanmar's legislature, a hangover from military rule which ensures that the army continues to hold sway.

Under Section 436, any significant changes to the constitution require a majority vote of more than 75 percent, giving the last word to soldiers.

During the parliamentary debate on Monday Colonel Htay Naing denied that the constitution had been written to bar Suu Kyi, adding that it was "not the time" to change 436.

Observers say the military, which kept Suu Kyi under house arrest for 15 years under the junta, has never wanted her to have a chance at the presidency.

One Myanmar expert, who asked not to be named, said the army has long made clear they are not supportive of constitutional reform and this position would remain, "irrespective of Obama's feelings on the matter".

"But the fact that they have also made their own suggestions for changes means they don't see the constitution as a sacred text that cannot be altered. That's significant," he told AFP.

The NLD this year gained the signatures of around five million people on a petition to end the army's veto on amending the charter.

Myanmar's reform drive has lost much of its sheen in recent months, as efforts to end its multiple ethnic wars foundered and activists raised growing concerns that the nation is rolling back on rights issues.

Shwe Mann, a former general who has previously indicated his own desire to stand for the presidency as head of the ruling party, said he was open to changing 59f, adding that amendment of the clause was not just to help "my friend" Suu Kyi.

"I want all citizens to get their full rights... the president's position is for the person able to work in the best interests of the people and the country," he added.