The assault in the city of Homs targeted a graduation ceremony and killed 89 people including personnel and civilians, according to the government. The Syrian Observatory for Human Rights, a war monitor, reported more than 120 dead.

- What happened? -

The drone attack happened at the end of the ceremony, as officers and their families were celebrating.

"People were smiling and taking photos. Suddenly, there was an explosion. We didn't know what happened," said Sleiman Assaf, 69, who had come to see his nephew graduate.

"People started to run like crazy, bodies were lying on the ground. Then I passed out. I woke up in hospital, where I was surrounded by people crying," he told AFP, as he waited for his nephew's funeral on Friday.

Videos circulating on social media have showed panic and chaos during the attack, with people falling to the ground and others pleading for help.

Defence Minister Ali Mahmoud Abbas was at the ceremony but left just minutes before the attack, an eyewitness and the Observatory said.

- Who launched the attack? -

No group has claimed responsibility for the assault, but Syrian authorities have blamed "armed terrorist organisations supported by known international actors", without elaborating.

The army has since bombed Syria's northwestern Idlib area, home to the country's last bastion of armed opposition.

Allied Russian forces also carried out air strikes Friday on the Idlib region, which is controlled by Hayat Tahrir al-Sham (HTS), a jihadist group led by Al-Qaeda's former Syria affiliate.

The Observatory said that at least 16 civilians have been killed so far.

Jihadist groups in the area have used drones against Syrian forces and their Russian allies before, but never with such bloody results.

Analyst Aron Lund of the Century International think tank said details were still too thin to speculate about the perpetrators.

"We've seen a lot of drone attacks coming out of Idlib in the past, including to target Russian aircraft at the Hmeimim base on the coast, but the details about who operated those drones were always kind of murky," he said.

"Is it (Hayat) Tahrir al-Sham, is it Turkey, a combination of both?" he asked.

The Islamic State group was defeated territorially in Syria in 2019, but its remnants launch assaults from desert hideouts, including in Homs province.

Syria's opposition in exile has suggested the government itself was responsible, but Lund dismissed the idea, saying that "it strains credibility to think the regime would wipe out such a big cohort of its own officers".

Observatory chief Rami Abdel Rahman would not be drawn on who might have been behind the attack, but said the drones could have been "assembled in Homs and launched from a location close" to the academy.

This could explain why they "evaded radars and air defence systems", he added.

- Why this target? -

Homs was a rebel bastion after the uprising against President Bashar al-Assad's regime broke out in 2011, spiralling into a complex war that drew in foreign armies and jihadists.

Government forces retook the city in 2017 and the province is now far from the front lines.

"The military is the backbone of Syria's regime, and the academy in Homs is where its officers are trained, ever since the creation of the Syrian state," said Lund.

Assad, his brother Maher, their late father Hafez al-Assad who took power in a 1970 coup, Syria's generals and other leading figures all passed through its doors, he added.

"Some of the people killed were undoubtedly from second or third generation military families," Lund said.

"This is home turf, it hits close to home for Syria's power elite, and I think the very strong official reactions need to be seen in that context," he added.