The strike hit a school in the village of Oe Htein Kwin -- around 100 kilometres (65 miles) northwest of the epicentre of the March 28 quake -- at about 10:00 am (0330 GMT), locals said.

UN chief Antonio Guterres is "deeply alarmed" by reports of the strike, his spokesman told reporters in New York, adding that "schools must remain areas in which children have a safe place to learn and not be bombed."

The green school building was a shattered husk on Monday afternoon, its metal roof crumpled with gaping holes blasted through its brickwork walls.

Over a dozen abandoned book bags were piled before a pole flying the Myanmar flag outside, as parents chiselled small graves out of the hard earth to bury the shrouded bodies of their children.

"For now 22 people in total -- 20 children and two teachers -- have been killed," said a 34-year-old teacher at the school, asking to remain anonymous.

"We tried to spread out the children, but the fighter was too fast and dropped its bombs," she added. "I haven't been able to collect all the casualty data as parents are in a rush."

An education official from the area of the village in Sagaing region gave the same toll.

The junta information team said reports of the strike were "fabricated news".

"There was no airstrike on non-military targets," it said in a statement.

Myanmar has been riven by civil war since the military deposed a civilian government in 2021, with the junta suffering stinging losses to a myriad of anti-coup guerillas and long-active ethnic armed groups.

But the military pledged a ceasefire throughout this month "to continue the rebuilding and rehabilitation process" after the magnitude 7.7 quake in Myanmar's central belt that killed nearly 3,800 people.

- 'Needs are immense' -

Tens of thousands are still living outside after the catastrophic jolt demolished or badly damaged their homes, facing the prospect of the monsoon season starting in the coming weeks.

"The needs are immense," Jagan Chapagain, secretary general of the International Federation of Red Cross and Red Crescent Societies, told AFP on Monday.

"My worry is that time is not on our side."

The United Nations and independent conflict monitors say the junta has continued its campaign of aerial bombardment despite the armistice meant to alleviate suffering.

Last week, the UN said that since the earthquake more than 200 civilians had been killed in at least 243 military attacks, including 171 airstrikes.

In its ceasefire declaration, the military warned it would take "necessary defensive measures" if pressed by its opponents.

Numerous anti-coup and ethnic armed groups have made own pledges to pause hostilities.

However during the truce some residents in eastern Myanmar said they have been displaced as anti-coup forces besieged junta-held towns on a lucrative trade route towards neighbouring Thailand.

The March earthquake saw the ground shear up to six metres (20 feet) in places, according to NASA analysis -- levelling apartments, opening yawning holes in roads and collapsing one major bridge.

The relief response is also being hobbled by funding shortfalls after US President Donald Trump slashed Washington's international aid budget.