BANGKOK (AP) — An entire Myanmar army battalion based near the Chinese border surrendered to an alliance of ethnic armed groups that launched a surprise offensive last month against the military, a spokesperson for one of the armed groups said Wednesday.

The surrender of 261 people — 127 soldiers and 134 of their family members — from the infantry battalion in northeastern Shan state appears to be the biggest by regular army forces since widespread armed conflict in Myanmar broke out in 2021 after the military seized power from the elected government of Aung San Suu Kyi in February that year.

The alliance expects to soon capture Laukkaing, the area’s major city, the spokesperson said.

The surrender — which has not been announced by the military government and could not be independently confirmed by The Associated Press — came two weeks after the Arakan Army, the Myanmar National Democratic Alliance Army and the Ta’ang National Liberation Army, calling themselves the Three Brotherhood Alliance, launched a coordinated offensive against the military government on Oct. 27.

The alliance has claimed widespread victories and the military government made a rare acknowledgement on Nov. 2 that it had lost control of three towns, one of which is a major border crossing for trade with China.

The offensive in the northern part of Shan state was seen as a significant challenge for the army, which has struggled to contain a nationwide uprising by members of the Peoples’ Defense Force, a pro-democracy armed group established after the 2021 army takeover. The various PDF groups that operate around the country have joined forces with well-organized, battle-hardened ethnic armed groups — including those in the Three Brotherhood Alliance — that have been fighting Myanmar’s central government for greater autonomy for decades.

The military government faced another challenge on Monday when the Arakan Army launched surprise attacks on military targets in five townships in Myanmar’s western Rakhine state. A yearlong cease fire had previously been declared in the state between the military government and the Arakan Army.

Le Kyar Wai, a spokesperson for the Myanmar National Democratic Alliance Army, told the AP on Wednesday that each of the soldiers who surrendered in Shan state, including the commander, was awarded 1 million kyat (about $480) and their family members were each given 100,000 kyat ($48).

“We give medical treatment to the injured. We delivered them safely to their desired destination,” Le Kyar Wai said, adding that the alliance groups planned to launch an operation soon to seize Laukkaing after they surrounded the city.

Laukkaing is known for hosting major organized criminal enterprises including cyberscam operations controlled by Chinese investors in cooperation with local Myanmar warlords.

The Chinese government in recent weeks has pushed a crackdown on these operations, and thousands of people involved have been repatriated to China. Many employed in the scams were tricked into working for them and then held against their will.

The Three Brotherhood Alliance had announced that one of the goals of its Oct. 27 offensive was to crack down on the scam operations. Le Kyar Wai said the alliance would rescue those held by the scam centers, arrest the people behind the operations and transfer them to relevant authorities, whom he did not specify but probably means Chinese law enforcement officials.

The soldiers who surrendered were not the first to lay down their weapons to the alliance groups in Shan state. On Oct. 30, 41 soldiers from another infantry battalion based in nearby Kunlong township surrendered to them. In total, more than 200 soldiers and police have surrendered to the alliance groups since Oct. 31, the groups said in a statement on Tuesday.

Since the offensive began last month, soldiers and police have also surrendered in Karen, Kayah, Rakhine and Chin states and Sagaing region, according to ethnic armed groups and independent local media.