A rare bombing of an army bus in Damascus and shelling shortly after of a town in rebel-held northwest Syria killed at least 27 people Wednesday, in the deadliest flare-up in months.

Two bombs planted on an army bus in central Damascus were detonated early in the morning, killing 14 people, in the worst such attack in the capital in four years, state news agency SANA reported.

Map locating Damascus in Syria where a bomb hit a bus carrying troops on Wednesday, according to state media Map locating Damascus in Syria where a bomb hit a bus carrying troops on Wednesday, according to state media Photo: AFP / STAFF

There was no immediate claim for the bombing, but government shelling shortly after killed 13 people in Idlib province, parts of which are controlled by groups that have claimed such attacks in the past.

"A terrorist bombing using two explosive devices targeted a passing bus" at a key bridge in Damascus, the state news agency said, reporting that at least three people were wounded.

Images released by SANA showed first responders searching the charred carcass of the bus and what it said was a bomb squad defusing a third device in the same area.

IMAGES TO COMPLETE VIDI9Q22MY_EN / VIDI9Q22CZ_EN Emergency services clean the site of a bomb attack on an army bus in Damascus killing at least a dozen people in the bloodiest such attack in years, state news reported. IMAGES TO COMPLETE VIDI9Q22MY_EN / VIDI9Q22CZ_EN Emergency services clean the site of a bomb attack on an army bus in Damascus killing at least a dozen people in the bloodiest such attack in years, state news reported. Photo: AFPTV / Youssef KARWASHAN

SANA quoted a military source as saying the bombs were detonated as the bus passed near the Hafez al-Assad bridge, close to the national museum in the heart of the capital.

"We hadn't seen violence of that type in a long time," a fruit vendor who gave his name as Salman told AFP at the scene.

"We thought we were done with such attacks. I hope this will be the last bombing."

Mangled metal is all that is left of the seating after a bomb blast rips through an army bus in Damascus Mangled metal is all that is left of the seating after a bomb blast rips through an army bus in Damascus Photo: AFP / -

Damascus had been largely spared such violence in recent years, especially since troops and allied militias retook the last significant rebel bastion near the capital in 2018.

Municipal workers clean up after the bombing with a roadside portrait of Syrian President Bashar al-Assad looming in the background Municipal workers clean up after the bombing with a roadside portrait of Syrian President Bashar al-Assad looming in the background Photo: AFP / LOUAI BESHARA

The attack is the deadliest in Damascus since a bombing claimed by the Islamic State jihadist group targeted the Justice Palace in March 2017, killing at least 30 people.

Around an hour after Wednesday's attack, Syrian army shelling struck the rebel-held town of Ariha in Idlib province.

Syrian troops stand guard as investigators inspect the charred carcass of the bombed out bus Syrian troops stand guard as investigators inspect the charred carcass of the bombed out bus Photo: AFP / -

The Syrian Observatory for Human Rights said rockets struck a busy area as students were heading to school.

Four children were among 13 people killed, the Britain-based war monitor said.

It was the highest civilian toll since a March 2020 truce deal brokered by Turkey and Russia effectively put fighting in Idlib on standby, the Observatory said.

Debris fills the streets of the rebel-held Syrian town of Ariha after shelling by government forces kills eight people, three of them children, just as pupils are headed to school Debris fills the streets of the rebel-held Syrian town of Ariha after shelling by government forces kills eight people, three of them children, just as pupils are headed to school Photo: AFP / Mohammed AL-RIFAI

"At 8 am (0500 GMT) we woke up to the bombardment. The children were terrified and were screaming," said Bilal Trissi, a father of two who lives nearby.

"They bombed us in our neighbourhood and in the market. There are children who died and people who lost their limbs... We don't know why, what are we guilty of?"

The UN children's agency condemned the shelling, calling it a "reminder that the war in Syria has not come to an end".

The Damascus bombing too will challenge the government's assertion that the decade-old war is over and stability guaranteed for reconstruction efforts and investment projects to begin in earnest.

President Bashar al-Assad's regime has been striving to claw itself out of international isolation and had been making inroads in recent months.

Iran's foreign ministry condemned the "cowardly" Damascus attack, saying it "will not undermine the determination of the Syrian government and people in their fight against terrorism."

The conflict that erupted with the brutal repression of unarmed protests demanding regime change in 2011 has left around half a million people dead.

Assad's position once hung by a thread, but Russia's military intervention in 2015 marked the start of a long and bloody fightback.

Government forces, also backed by Iran and its proxy militias, have recaptured nearly all key cities in the country, with US-backed Kurdish forces still running the northeast.

The IS group's "caliphate" that once straddled swathes of Syria and Iraq shrank to its death in eastern Syria in early 2019.

Since then, the government's main focus has been the Idlib region, now home to many rebels who were forced to surrender elsewhere.

It is dominated by the jihadist group Hayat Tahrir al-Sham (HTS), which includes leaders of Al-Qaeda's former Syria franchise and over which Turkey has some sway.

Also Wednesday, six members of a pro-government militia were killed in an arms depot blast in the central province of Hama, the Observatory said.

The pro-government Al-Watan daily reported the same death toll and said a "technical error" caused the explosion, without elaborating.