Delegates from one of Myanmar's most heavily armed ethnic groups stormed out of peace talks on Thursday in an early blow to a landmark gathering aimed at ushering in a new era of peace.

The five-day conference in the capital Naypyidaw has been hailed as the best chance in a generation for Myanmar to end wars that have raged for up to 70-years, claiming thousands of lives and keeping the country mired in poverty.

Among the militias attending is the powerful 20,000-strong United Wa State Army.

They stopped fighting the government years back in exchange for control of a remote portion of territory bordering China which is now a notorious drug manufacturing hub.

They had originally refused to make this week's talks, arguing they signed their own ceasefire with the previous military government back in 1989.

But they eventually agreed to attend following discussions last month with de facto leader Aung San Suu Kyi and after pressure was applied by China, which retains significant influence over the group.

Yet on day two of the talks four UWSA delegates walked out, officials said, reportedly after being told they could not address the gathering.

Government peace negotiator Khin Zaw Oo said the Wa had been given observer badges, instead of ones allowing them to speak, angering their delegation.

But he played down their departure, saying it was a "misunderstanding" that could be solved.

- Discrimination -

A spokesman for the Wa militia told the Democratic Voice of Burma the group left after being told they were only accredited as observers, calling it discrimination.

But Lian Hmung Sahkong, from the Chin National Front, another ethnic group at the talks, denied the Wa were treated unfairly.

"We give equal rights to them and gave them a front row seat. I would like to confirm again that we did what they demanded," he said.

Suu Kyi has been informed of the episode and "gave instructions that the peace process not be harmed because of this case", government spokesman Zaw Htay told reporters, without elaborating.

The veteran democracy activist has devoted her first few months in power to planning the summit, where she hopes to thrash out the precepts of a federal state in exchange for peace.

Several complex ethic conflicts are rumbling across Myanmar's borderlands, hampering efforts to build the country's economy after the end of junta rule.

While the Wa have not fought against the military for years, they are accused of producing and trafficking huge amounts of methamphetamine and heroin from their secretive holdout and buying weapons with the proceeds.

A leaked version of a speech they prepared seen by an AFP reporter expressed scepticism that a singular agreement could address the diverse political aspirations of each ethnic group.

The speech also called for a "high degree of autonomy" in minority regions and demanded the army withdraw from politics altogether.

While Myanmar's military stepped down from junta rule in 2011, soldiers are still gifted a quarter of parliament seats -- an effective veto over any efforts to amend the nation's charter.