NAYPYIDAW, (Myanmar): Myanmar's security forces killed nearly 90 people in the bloodiest day since the military seized power, a monitoring group said Saturday, as the junta staged a major show of might for its annual Armed Forces Day. 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.

But by nightfall, the country had seen its deadliest day since the coup, with local monitoring group Assistance Association for Political Prisoners (AAPP) confirming 89 people were killed by "early evening". Britain's foreign secretary called the day "a new low" for the junta, and the embassies of the United States, the European Union and the United Kingdom all condemned the bloodshed. Speaking to eyewitnesses and rescue workers, AFP has independently verified that at least 25 people were killed.

Violence erupted all over the central Mandalay region as security forces opened fire on protesters, killing at least 10 in five different cities - one of them a 14-year-old girl in Meiktila.

"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.

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.

"Today's killing of unarmed civilians, including children, marks a new low," said UK foreign secretary Dominic Raab on Twitter. "We will work with our international partners to end this senseless violence, hold those responsible to account, and secure a path back to democracy." The UN human rights high commissioner's office said it had received reports of "scores killed", adding that "this violence is compounding the illegitimacy of the coup and the culpability of its leaders". The European Union delegation in Yangon called Saturday "a day of terror and dishonour", while the US embassy said the security forces' actions were akin to "murdering unarmed civilians", adding "these are not the actions of a professional military or police force".

Saturday's bloodshed pushed the current death toll since the coup to nearly 420, according to AAPP's numbers. 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 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".