The Myanmar soldier, wearing his crisp green uniform, rifles through a box of T-shirts for a souvenir of his time in the country's fledgling legislature -- a deeply controversial position in the former junta-run nation on the cusp of key elections.

With a quarter of parliamentary seats and an effective veto on opposition leader Aung San Suu Kyi's presidential hopes, unelected military men have a major role in the country's delicate political transition, regardless of the result of landmark polls later this year.

Suu Kyi has said reforms are stalling and refuses to rule out a boycott of the election, expected in early November this year, as she fights to change the junta-era constitution which bars her from the top job.

While the army is reluctant to further relinquish its political leverage, observers say the hundreds of soldiers who have sat in parliament have been exposed to lively debate and compromise like never before.

"It is interesting," the soldier told AFP of his experience in the legislature, asking not to be named.

"We serve here as a duty, appointed by the Tatmadaw (army)," he said, after finally selecting a T-shirt bearing a picture of the massive parliament building in the remote capital of Naypyidaw.

- Military might -

Myanmar's army seized power in 1962 and ruled by force for nearly half a century, steering the formerly rich country into isolation and poverty.

Criticism was crushed, with bloody crackdowns on mass protests in 1988 and 2007, the jailing of hundreds of dissidents and draconian media censorship.

In 2011 the country's junta rulers dramatically stepped aside in favour of a quasi-civilian government, which has ushered in sweeping reforms despite remaining dominated by retired generals.

Those changes -- including the release of political prisoners, untethering of the press and opening up of the economy -- stunned the international community and lured in hordes of foreign investors.

An International Crisis Group report released in late April said the military "initiated the transition and continues to back it".

But it said that while the army chief has pledged to ensure credible elections, its "expectations are unclear". The army also retains significant powers, including control of key security ministries.

Suu Kyi, whose party is expected to sweep the elections, is ineligible for the presidency because the army-drafted constitution excludes those with foreign children from top office. Her two sons are British, as was her late husband.

The military has vowed to prevent major constitutional amendments.

It has the last say on charter changes because of rules that require more than a three-quarters majority for significant amendments.

And on these issues they will vote together.

"When it comes to some things, some sections, we are organised," military MP Brigadier General Htay Naing told AFP, in a rare interview at parliament recently.

But he said army MPs were entitled to vote freely on other matters.

The military contingent of MPs -- selected by the army chief and shuffled periodically -- had evolved over the years, he added.

"In the past, there were many young people. They didn't understand much. Now we have more seniors and so they are more knowledgeable," he said.

The appointment of higher-ranking officers to parliament in 2012 also suggests an "evolution" in the understanding of their role, according to Renaud Egreteau, a visiting fellow at the Institute for Southeast Asian Studies in Singapore who has conducted research on Myanmar's parliament.

While they have proved "increasingly engaged in discussions", especially in closed-door parliamentary committees, he said they remained "relatively quiescent backbenchers" and were likely to stay as such until after the election.

But he said their behaviour may change if "the preserves of the military parliamentary bloc become increasingly challenged by fellow elected representatives -- or a new government".

- Back to the barracks? -

Suu Kyi has a complex relationship with an army that kept her under house arrest for over 15 years.

Her independence hero father is credited with founding the country's modern military, and in 2013 the Nobel peace laureate admitted she was "fond" of the army -- despite her detention, and despite a litany of allegations of rights abuses, particularly in Myanmar's ethnic conflicts.

"As she is the daughter of General Aung San, there is no reason not to respect her personally. But the action and attitude of her and her party are sometimes different from ours," Htay Naing said.

Suu Kyi has said that allowing soldiers to remain indefinitely in parliament is "not democracy", but is advocating a gradual reduction in the proportion of army MPs -- a pragmatic position in a country and region blighted by military coups.

Even the army admits it will one day need to retreat to the barracks.

"There will be a time when we are not needed here anymore," said Htay Naing, adding however that the country's decades of ethnic conflict, still raging in some areas, justified the military's continued presence in politics.

With Suu Kyi barred from the presidency, observers say the tussle for the top job may still end up between two ex-generals -- current President Thein Sein and parliamentary speaker Shwe Mann -- while the sitting army chief Min Aung Hlaing is also thought to harbour political aspirations.

And with no timetable for a transfer to full civilian control, the men in green seem set to be a feature of Myanmar's political landscape for the foreseeable future.