Funerals held for victims of attack on military academy during graduation ceremony.

Coffins draped in Syrian flags on Friday lined the streets outside the Homs military hospital as a military band played somber music and soldiers saluted.

On Thursday, several drones attacked a graduation ceremony in the academy’s courtyard, where families had gathered with the new officers.

Syria’s Ministry of Health said at least 89 people had been killed, including 31 women and five children. The Syrian Observatory for Human Rights, which monitors the Syrian conflict, put the toll at above 120. Syria has declared three days of national mourning.

There have been no claims of responsibility for the attack, and Syria’s Ministries of Defence and Foreign Affairs and Expatriates blamed what they described as “terrorist” groups without providing specifics. They promised to respond “with full force”.

Throughout the night and into the early morning on Friday, Syrian government troops blasted artillery shells into rebel-held territory in the northern provinces of Idlib and Aleppo, according to the observatory and the civil defence group known as the White Helmets, which operates in opposition-held areas.

Thursday’s strike was an unprecedented use of drones against government forces in the war, which began with protests against President Bashar al-Assad in 2011 and spiralled into a conflict that has killed hundreds of thousands of people and displaced millions.

Al Jazeera’s Zeina Khodr, who has reported extensively on Syria, said the attack represented “a major security breach, a blow to the Syrian regime”.

“It has been years since the forces of the Syrian president, Bashar al-Assad, have been targeted in such an operation in the heart of government-controlled territory,” she said.

“It seems that the Syrian regime is blaming the opposition because just moments after this attack, their planes started to target residential areas in the opposition-controlled enclaves in the northwest of the country,” she added.

United Nations Secretary-General Antonio Guterres “expressed deep concern” over the drone attack in Homs as well as “reports of retaliatory shelling” in northwest Syria, his spokesperson Stephane Dujarric said.

Meanwhile, Russian President and Syrian government ally Vladimir Putin sent his condolences to al-Assad, Lebanese station Al-Manar reported on Friday.