Myanmar's military has battled ethnic minority and other insurgencies for decades but a 2021 coup has brought unprecedented coordination between anti-military forces that are mounting the biggest challenge to the army in years.

Junta spokesperson Zaw Min Tun said the military was facing "heavy assaults from a significant number of armed rebel soldiers" in Shan State in the northeast, Kayah State in the east and Rakhine State in the west.

Zaw Min Tun said some military positions had been evacuated and the insurgents had been using drones to drop hundreds of bombs on military posts.

"We are urgently taking measures to protect against drone bomb attacks effectively," the junta spokesperson said late on Wednesday.

In the capital, Naypyitaw, government staff have been ordered to form units to respond to "emergency" situations, said Tin Maung Swe, secretary of Naypyitaw Council.

He denied that the order was in response to the security situation, saying the capital was calm.

"This is the plan to help in the event of an emergency, especially natural disasters," Tin Maung Swe told Reuters.

A parallel government formed by pro-democracy politicians to oppose the military, and allied with some insurgent factions, has launched a "Road to Naypyitaw" campaign which it says is aimed at taking control of the capital.

Separately, the military's State Administration Council (SAC), in an order on Wednesday, said all those with basic military training should be ready to go and serve, Khit Thit media reported.

Reuters could not independently verify the document.

UN CONCERN

Myanmar has been in turmoil since the 2021 coup, when the military ousted a government led by Nobel laureate Aung San Suu Kyi, ending a decade of tentative democratic reform.

The military ruled Myanmar with an iron fist for 50 years after seizing power in 1962, insisting it was the only institution capable of holding the diverse country together.

The 2021 coup dashed hopes for reform and triggered a groundswell of opposition that has united pro-democracy activists in towns and cities with ethnic minority forces fighting for self-determination in hinterlands.

Clashes have sent refugees into all of Myanmar's neighbours, including thousands who fled into India in recent days from fighting in Chin State in the northwest.

Western governments have re-imposed sanctions on the Myanmar junta in response to the coup and crackdowns on protests and demanded the release of Suu Kyi and other pro-democracy politicians and activists.

Myanmar's Southeast Asian neighbours have tried to encourage a peace process but the generals have largely ignored their efforts.

U.N. Secretary General Antonio Guterres was deeply concerned by the "expansion of conflict in Myanmar" and called for all parties to protect civilians, a spokesperson said.

"The number of displaced people in Myanmar now exceeds 2 million," the spokesperson said.

The Arakan Army (AA) rebel group fighting for autonomy in Rakhine State said on Wednesday that dozens of police and military men had surrendered or been captured as its forces advanced.

The junta spokesperson denounced the group saying it was "destroying" Rakhine State.

Separately, a video posted on social media by anti-military forces in Kayah State, and verified by Reuters, showed wounded junta troops surrendering to insurgents, who were seen offering medical help.

"We are ready to shoot you right now but we won't do that. You raise the white flag and walk out, nothing will happen to you," a fighter who identified himself as the vice commander-in-chief of the rebel Karenni National Defence Force is heard telling the junta soldiers.