Relatives and officials gathered in the central Syrian city of Homs on Friday morning for the first funerals of dozens of people killed in a drone attack on a military academy.

Thursday's aerial assault came just after the end of a graduation ceremony for officers, and wounded both military personnel and their families.

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

An AFP correspondent said dozens of distraught victims' relatives had gathered outside the Homs military hospital since the early morning.

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.

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

No group has claimed responsibility for the attack, but the Syrian army on Thursday accused "armed terrorist organisations" of the attack that was carried out by "explosive-laden drones", vowing to "respond with full force".

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

In the rebel-held Idlib region, the last pocket of armed opposition in northwest Syria, residents reported heavy bombardment by government forces in apparent retaliation.

The Observatory said Friday that 15 civilians had been killed, raising an earlier toll.

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

The jihadist group has used drones to attack government-held areas in the past.

United Nations chief Antonio Guterres was "deeply concerned" over the drone attack and the retaliatory shelling, his spokesman Stephane Dujarric said.

The government has declared three days of mourning starting Friday.