Separately, Turkey carried out fresh raids in the country's Kurdish-controlled northeast, targeting energy infrastructure, with the death toll rising to 15 over two days, Kurdish officials said.

In one of the bloodiest single attacks on the army since the start of Syria's war in 2011, Thursday's assault came just after the ceremony attended by officers and their families, killing and wounding both military personnel and civilians.

State media said Friday that 89 had died, including 31 women and five children, with 277 other people wounded.

Dozens of distraught victims' relatives gathered outside the Homs military hospital since the early morning, an AFP correspondent said.

A woman in a black dress adorned with white flowers was overwhelmed with grief at the loss of her son.

"Do not go, my beloved," she cried. "This sleep does not befit you."

The Syrian Observatory for Human Rights, a Britain-based monitor, reported a heavier toll of 123 dead, including 54 civilians, 39 of them women and children. It said at least 150 people were wounded.

In a rare move since the war broke out, the government has declared three days of mourning starting Friday, with flags flying at half-mast.

Defence Minister Ali Mahmoud Abbas attended the first funerals for around 30 people, including both military and civilians.

Military personnel saluted as rows of caskets draped in Syrian flags were carried one by one and placed into ambulances for transportation for burial.

The conflict in Syria has killed more than half a million people and displaced millions since it began in 2011, spiralling into a devastating war involving foreign armies, militias and jihadists.

- Panic and chaos -

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

"Martyrdom, dignity and national pride come at a great cost," Abbas told victims' families, according to a statement broadcast on state television.

The blood of those who died "is dear, but the nation is dearer", he added.

Abbas had been present at the graduation ceremony but left just minutes before the attack, an eyewitness and the Observatory said.

At the military hospital, Khawlah, 33, was searching among the coffins for her brother.

"Amjad did not die, I died," she told AFP, grief-stricken.

No group has claimed responsibility for the assault, but the Syrian army has accused "armed terrorist organisations" of the attack with "explosive-laden drones", vowing to "respond with full force".

The Syrian army on Thursday began a bombing campaign on opposition-held areas in the country's northwest in apparent retaliation.

The Observatory said Friday that 15 civilians had been killed, adding that warplanes of government ally Russia carried out at least five strikes in the Idlib area, leaving a child dead.

Aron Lund of the Century International think tank said President Bashar al-Assad and other family members trained at the Homs academy, meaning the attack "hits close to home" and "the very strong official reactions need to be seen in that context."

Russian President Vladimir Putin condemned the attack, expressed his condolences to Assad, and pledged "to keep up our close cooperation" against "terrorism", the Kremlin said.

- Turkish strikes -

Homs province was an opposition stronghold early in Syria's conflict but has been in government hands for several years.

Swathes of Idlib province and areas bordering Aleppo, Hama and Latakia provinces are controlled by Hayat Tahrir al-Sham, led by Al-Qaeda's former Syria branch.

HTS and the Islamic State jihadist group have used drones to attack government-held areas and Syrian and Russian military targets, including in recent months, according to the Observatory.

Thursday's attack came as Turkey began strikes in northeast Syria, hitting military and civilian targets including energy infrastructure, according to officials in the semi-autonomous Kurdish administration that controls the area.

Ankara had threatened retaliation for a bomb attack Sunday in the capital that wounded two security officers and was claimed by a branch of the banned Kurdistan Workers' Party (PKK), which Turkey and its Western allies view as a terrorist organisation.

The US-backed, Kurdish-led Syrian Democratic Forces (SDF) said Friday that 15 people had been killed in the northeast Syria strikes over two days, including eight civilians.

Turkey views the Kurdish People's Protection Units (YPG) that dominate the SDF as an offshoot of PKK.

Turkey's defence ministry said Friday that a soldier had died following a rocket attack on a Turkish military base in the northern Syrian town of Dabiq.