Ethnic insurgents launched fresh attacks across northern Myanmar on Thursday, burning a police post and killing at least one civilian staff member at an elite military college, an army spokesman said.

The Northern Alliance, a collective of armed groups active in the region, claimed responsibility for the attacks on the Defence Services Technological Academy in Pyin Oo Lwin, western Shan state, and four other targets.

Army spokesman Tun Tun Nyi said soldiers were fighting insurgents in Naung Cho township near the Gokteik viaduct, a towering railway bridge built under British colonial rule.

Another bridge had been destroyed by insurgents who also burned down the township's narcotics police office, he said.

"There are casualties... but we cannot confirm the number yet," he told Reuters by phone.

Fighting was also reported at a toll gate on the highway to Lashio, the largest town in Shan state, a fire services official said.

The attacks mark a major escalation in a decades-old conflict in the region, where several groups are fighting for greater autonomy for ethnic minorities.

Pyin Oo Lwin, a military town and former British hill station outside the city of Mandalay, had until Thursday been unaffected by renewed fighting in the region.

A months-long ceasefire agreement that ended in June was recently extended until Aug. 31.

A spokesman for the Northern Alliance said it was responding to recent army action in ethnic areas.

"We aim to change battlefronts, as the Burmese military are increasing their offensives in ethnic areas during these days," spokesman Mong Aik Kyaw told Reuters by phone.

"The Aung San Suu Kyi-led ... government is trying to make peace, but nothing can happen if the military doesn't participate in it," he added.

The renewed fighting is a further setback for civilian leader Aung San Suu Kyi's bid bring peace to the country amid a stuttering transition from full military rule.

The Nobel laureate came to power following a landslide election win in late 2016, vowing to prioritize peace talks between ethnic armed groups, the military and civilian government.

But the conflict has escalated in northern Kachin and Shan states as well as the western Rakhine region on the border with Bangladesh.

Most recently, government troops have been locked in fierce fighting in Rakhine with insurgents belonging to the Arakan Army, a group that recruits mostly from the Buddhist Rakhine majority in the area.

A spokesman for the Arakan Army, which is allied with the Northern Alliance, said its troops joined in Thursday's attacks. "We made a counter-attack against the Burmese army, as they did offensive attacks in the land of our comrades," said Arakan Army spokesman Khine Thu Kha. "They announced ceasefires but attacked wherever they wanted to," he added.