The junta has increased air strikes year-on-year since the start of Myanmar's civil war, conflict monitors say, after snatching power in a 2021 putsch ending a decade-long democratic experiment.

The military has set polls starting December 28 -- touting the vote as an off-ramp to fighting -- but rebels have pledged to block it from territory they control, which the junta is battling to claw back.

A military jet bombed on Wednesday the general hospital of Mrauk-U in western Rakhine state, bordering Bangladesh, two aid workers said.

A junta spokesman could not be reached for comment.

At least 20 bodies were visible on the ground outside the hospital overnight, while daybreak revealed rubble covering ward beds, masonry peppered by shrapnel and the nearby ground cratered.

"This is an inhuman act. It is vile and violent," said aid worker Wai Hun Aung, who arrived on the scene on Thursday morning.

He said 31 people were killed and 68 wounded. A separatist force gave a toll of 33 dead.

"They are saying that they will hold elections on December 28," the aid worker added. "Even at this time, they are brutally killing the people."

Health workers and patients were killed, and "hospital infrastructure was severely damaged, with operating rooms and the main inpatient ward completely destroyed," said World Health Organization chief Tedros Adhanom Ghebreyesus on X.

- Mass mourning -

Carpenter Maung Bu Chay said the strike killed three of his wife, and his daughter-in-law and her father.

"When someone informed me they were in the completely destroyed building, I realised they hadn't survived," said the 61-year-old.

"I feel resentful about their act. I feel strong anger and defiance in my heart."

Locals hammered together plywood coffins outside a funeral hall where bodies lay inside, as mourners wept on their knees in a frenzy of grief.

Hla Maung Oo, the chair of a local committee that organises free funerals, said the death toll of 31 included a months-old infant.

"We don't want this to happen again," he said. "It should not happen like this."

Rakhine state is controlled almost in its entirety by the Arakan Army (AA), an ethnic minority separatist force active long before the military toppled the civilian government of democratic leader Aung San Suu Kyi.

The separatist force said in a statement that 33 people were killed and 76 wounded in the strike.

- State of decline -

The Arakan Army has emerged as one of the most powerful opposition groups in the civil war ravaging Myanmar, alongside other ethnic minority fighters and pro-democracy partisans who took up arms after the coup.

Scattered rebels initially struggled to make headway before a trio of groups led a joint offensive starting in 2023, backfooting the military and prompting it to bolster its ranks with conscripted troops.

The AA was a key participant in the so-called "Three Brotherhood Alliance" but its two other factions this year agreed Chinese-brokered truces, leaving it as the last one standing.

While the military-run election has been widely criticised by monitors including the United Nations, Beijing has emerged as a key backer, saying it should "restore social stability" to its neighbour.

The AA has proven a powerful adversary for the junta and now controls all but three of Rakhine's 17 townships, according to conflict monitors.

But the group's ambitions are largely limited to their Rakhine homeland, hemmed in by the coast of the Bay of Bengal and jungle-clad mountains to the north.

The group has also been accused of atrocities including against the mostly Muslim Rohingya ethnic minority from the region.

Meanwhile the military has blockaded Rakhine, contributing to a humanitarian crisis which has seen "a dramatic rise in hunger and malnutrition", the World Food Programme said in August.