The vote was the climax of a year of fierce debates between MPs as the civilian government attempted to reform the constitution and reduce the military's stranglehold on parliament.

The country is gearing up to polls likely to be held later this year, only the second since outright military rule came to an end.

But the military still wields considerable power, appointing three key ministers -- defence, border and home affairs.

Crucially, it holds a quarter of parliamentary seats, effectively giving it a veto over any legislation.

Suu Kyi's ruling National League for Democracy (NLD) has been fighting for reforms of the military-scripted 2008 constitution.

In unprecedented scenes in Myanmar's young parliament, the tempers of civilian and military MPs have frayed during discussions of the amendments, with MPs shouting at each other across a normally staid chamber.

The proposal to slash the number of seats reserved for the military came up on the opening day of a marathon series of votes expected to last nearly two weeks.

In the end, it was voted down by 633 votes to 404.

NLD MP Aung Thein told AFP his party had anticipated the loss but had a duty to live up to its pledges to voters ahead of its landslide victory in 2015.

"We would like the people to know we tried," he said.

Emotions have been at fever pitch on both sides with rallies of both nationalists supporting the military and Suu Kyi's followers calling for reform.

Another key vote Wednesday will be held on whether to strike down a clause widely thought to target Aung San Suu Kyi, banning anyone with foreigners as immediate family from becoming president

Even though Suu Kyi's late husband was British and her two sons are British citizens, her party circumvented the rule by creating her position of state counsellor outside of the constitution.

In a counter proposal, the military instead seeks to extend the clause to include any ministerial position, a move that would take away several portfolios held by Suu Kyi.

The proposed reform, however, stands virtually no chance of getting past an NLD-dominated parliament.

Independent Yangon-based analyst David Mathieson slammed the whole process as "pointless", saying it ignored measures that might help advance rights of minorities, decentralise politics and alleviate poverty.

"It's a stalemate based on arrogant self-interest, not the democratic reforms Myanmar needs."