Myanmar's junta has sentenced to death three high-ranking officers who oversaw the surrender of a strategic town on the Chinese border to ethnic minority fighters last month, military sources told AFP.

Hundreds of troops put down their weapons and handed over the town of Laukkai in Shan state to the so-called Three Brotherhood Alliance after months of fighting that saw the military lose swathes of territory.

The surrender was one of the biggest single losses for the military in decades, and sparked further criticism of the junta leadership by its supporters.

After the surrender, the officers and their troops were allowed to leave the area by the alliance.

"Three brigadier generals including the commander of Laukkai town were given the death sentence," a military source told AFP on condition of anonymity as they were not authorised to talk to the media.

Another military source confirmed the sentencing.

Three other brigadier generals were sentenced to life imprisonment for their role in the surrender at Laukkai, the two sources said.

Laukkai is the largest town seized by the Three Brotherhood Alliance -- made up of the Myanmar National Democratic Alliance Army (MNDAA), the Arakan Army (AA) and the Ta'ang National Liberation Army (TNLA).

The alliance launched a surprise offensive across a swathe of northern Myanmar in late October and has seized several towns and lucrative trade hubs along the border with China.

- Sex, drugs and scams -

Current junta chief Min Aung Hlaing made a name for himself in 2009 when, as a regional commander, he expelled the MNDAA from the Laukkai.

The army then installed a militia that enriched itself producing drugs and selling gambling and sex to visitors from across the Chinese border.

Laukkai later became notorious for online scam operations in which thousands of Chinese and other foreign nationals -- many of them trafficked and working under duress -- defraud their compatriots over the internet.

A source close to the MNDAA recently told AFP that the group was working to install a new administration in the town, without giving details.

The alliance's successes have galvanised so-called People's Defence Forces -- dedicated to reversing the 2021 coup that ousted Aung San Suu Kyi's elected government -- to launch attacks of their own across the country.

Analysts say the onslaught has put the embattled junta in its most vulnerable position since it seized power.

This month it announced it would begin conscripting young men and women into its ranks due to the "current situation".

No details have been given about how those called up would be expected to serve, but many young people are not keen to wait and find out.

Last week local media images showed hundreds of people queueing outside the passport office in Mandalay.

And in commercial hub Yangon, thousands of young men and women queued outside the Thai embassy seeking visas to get out of Myanmar last week.