Myanmar's military government has acknowledged that it withdrew its forces from a key city on the northeastern border with China after it was taken over by an alliance of ethnic armed groups it has been battling for months.

The Three Brotherhood Alliance took control of Laukkaing late Thursday after Myanmar military forces laid down their arms and were allowed to withdraw, both sides said on Saturday.

Photos and videos on social media showed a vast amount of weapons that the alliance claimed to have captured.

Laukkaing is the capital of the Kokang Self-Administered Zone, which is geographically part of northern Shan state in Myanmar.

The Three Brotherhood Alliance is comprised of the Myanmar National Democratic Alliance Army, the Ta'ang National Liberation Army and the Arakan Army. The MNDAA is a military force of the Kokang minority, who are ethnic Chinese.

The capture of the city was a primary goal of the alliance's offensive launched on October 27.

Myanmar government spokesperson Maj. Gen. Zaw Min Tun told the Popular News Journal, a pro-army website, on Saturday that the military and its local commanders relinquished control of Laukkaing after considering many aspects, including the safety of the family members of the soldiers stationed there.

He said the military also took into consideration Myanmar's relationship with China, which is just across the border from Laukkaing.

China, which has good relations with both the military and the ethnic alliance, has been seeking an end to the fighting.

Beijing protested after artillery shells landed in its territory on Wednesday, wounding five people. Zaw Min Tun said the alliance had fired the shells and that it tried to blame the military in order to damage its relationship with China.

A statement posted by the alliance on social media late Friday declared that the entire Kokang region had become a “Military Council-free area”.

It said 2,389 military personnel — including six brigadier generals — and their family members had surrendered by Friday and that all were evacuated to safety.

Video clips circulating on social media purportedly showed the soldiers and their family members being transported in various vehicles. The Shwe Phee Myay News Agency, an online news site reporting from Shan state, reported that many of them were taken to Lashio, the capital of Shan's northern region, under an agreement with the MNDAA for their repatriation.

The city's fall to the alliance is the biggest in a series of defeats suffered by Myanmar's military government since the offensive was launched, underlining the pressure it is under as it battles pro-democracy guerrillas and other ethnic minority armed groups across the country.

Ethnic armed organisations have battled for greater autonomy on and off for decades, but Myanmar has been wracked by what amounts to civil war since the army seized power in February 2021 from the elected government of Aung San Suu Kyi, sparking nationwide armed resistance by pro-democracy forces.

Whether the Three Brotherhood Alliance will try to extend its offensive outside of Shan state is not yet clear, but it has vowed to keep fighting against military rule.

The alliance cast its offensive as a struggle against military rule and an effort to rid the region of major organised criminal enterprises, including cyberscam operations controlled by Chinese investors in collusion with local Myanmar warlords, especially in Laukkaing. China has publicly sought to eradicate the large-scale criminal industry and tens of thousands of people involved have been repatriated to China in recent weeks.

But the offensive was also widely recognised as an effort by the MNDAA to regain control of the Kokang Self-Administered Zone by ousting a rival Kokang group backed by the military government from its seat of power.

Peng Deren, the MNDAA commander, said in a New Year's speech published by The Kokang, an affiliated online media site, that the alliance had seized over 250 military targets and five border crossings with China.

He said more than 300 cyberscam centres were raided and more than 40,000 Chinese involved in cyber crimes were repatriated to their country.