The nation has been in turmoil since the generals ousted and detained civilian leader Aung San Suu Kyi in February, triggering a major uprising demanding a return to democracy.

The country's capital Naypyidaw saw a grand parade of troops and military vehicles in the morning, with a speech by junta leader Min Aung Hlaing warning that acts of so-called "terrorism" were unacceptable.

By afternoon, as protesters continued to come out across Myanmar, AFP verified that at least 24 people were killed -- though local media put the death toll at far higher.

The embassies of the United States, the European Union and the United Kingdom all condemned the bloodshed.

Violence erupted all over the central Mandalay region as security forces opened fire on protesters, killing at least nine in four different cities -- one of them a doctor in Wundwin and a 14-year-old girl in Meiktila, according to rescue workers on the ground.

"Four men were brought to us dead," an emergency worker from Mandalay, Myanmar's second largest city, told AFP as she frantically tried to treat dozens of injured.

A protester in Myingyan, who witnessed a man killed when he was shot in the neck, said the death toll will likely grow as security forces have continued shooting across his city.

"Today is like a revolution day for us."

In Sagaing region, at least five were killed in two cities -- one of them a 13-year-old boy who was killed in the crossfire of a crackdown, according to a resident of Shwebo.

"He was just sitting inside his house," said the resident, adding that the teenager was supposed to become a novice monk.

In the northeastern Shan state, security forces opened fire on university students -- killing at least three -- while in the tourist city of Bagan, a march through ancient pagodas turned into mayhem when one protesting tour guide was shot dead.

- 'Day of terror and dishonour' -

"These are not the actions of a professional military or police force," said the US embassy in Myanmar Saturday on its Facebook page.

"On Myanmar's Armed Forces Day, security forces are murdering unarmed civilians, including children, the very people they swore to protect," it said, calling for the return of democracy.

"Myanmar's people have spoken clearly: they do not want to live under military rule."

The European Union delegation in Yangon called Saturday "a day of terror and dishonour", while former colonial power Britain also blasted security forces as having "disgraced themselves".

Saturday's bloodshed adds to the current toll of nearly 330 killed since the coup, according to a local monitoring group.

Across Yangon, plumes of smoke rose above the former capital which has emerged as a hotspot of unrest in recent weeks.

At least five were killed overnight after police opened fire when demonstrators gathered in front of a police station in the city's south to call for the release of their friends. Residents heard nonstop shooting though the night.

A baby playing on the street in a northern Yangon township was hit in the eye with a rubber bullet when police unleashed gunfire at nearby protesters. She was rushed to the hospital by her parents.

Further north near the notorious Insein prison, a pre-dawn rally -- which had protesters wearing bicycle helmets and shielded by sandbag barricades -- devolved into chaos when soldiers started shooting.

At least one was killed -- a 21-year-old police officer, Chit Lin Thu, who had joined the anti-coup movement.

"He was shot in the head and died at home," his father Joseph told AFP.

"I am extremely sad for him, but at the same time, I am proud of my son".

- 'Enemy of democracy' -

During a speech at the parade, junta leader General Min Aung Hlaing once again defended the coup and pledged to yield power after new elections.

But he also issued another threat to the anti-coup movement that has gripped the country since he took charge, warning that acts of "terrorism which can be harmful to state tranquillity and security" were unacceptable.

"The democracy we desire would be an undisciplined one if they pay no respect to and violate the law," he said.

Armed Forces Day commemorates the start of local resistance to the Japanese occupation during World War II, and usually accompanies a military parade attended by foreign officers and diplomats.

The junta announced that eight international delegations attended Saturday's event, including China and Russia -- with state media broadcasting Russian deputy defence minister Alexander Fomin in the audience.

According to Russian news agency Interfax, the defence ministry announced that Russian-made military equipment -- tanks, fighter jets, and helicopters -- were included in the parade.

A group of ousted parliamentarians working underground against the junta -- The Committee Representing Pyidaungsu Hluttaw (CRPH), the Burmese word for "parliament" -- condemned the show of might after a bloody seven weeks.

"We should not allow these military generals to celebrate after they killed our brothers and sisters," said its UN special envoy, who goes by the moniker Dr Sasa.

bur-dhc/reb

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