A powerful explosion on Wednesday killed 15 people including more than a dozen civilians in militant-held northwest Syria, a war monitor said, as rescuers searched for people trapped under the rubble.

A reporter at the scene saw a building of at least four storeys that had collapsed in the town of Jisr Al Shughur in Idlib, a region controlled by Syria’s former Al-Qaeda affiliate.

One opposite had partially caved in while surrounding buildings appeared on the verge of collapse.

A civil defence worker eased himself under a massive slab of fallen concrete to search for victims, as three colleagues crouched by his side to help.

Thirteen civilians were among those killed in the blast, the cause of which was not immediately clear, according to the Syrian Observatory for Human Rights, a Britain-based monitoring group.

“The explosion hit next to the market,” killing 15 people including the daughter of a Turkestani fighter, Observatory chief Rami Abdel Rahman said.

He earlier said the explosion could have been the result of a car bomb or a vehicle carrying explosives that detonated.

But bystanders and the head of the local civil defence unit, Abdelwahab Al Abdu, said they did not know what caused it.

Abdu said 13 civilians had died in “an explosion of unknown origin.”

Abu Ammar, a father of two, said he felt the “huge” blast from his home about 50m away.

“We ran to the place of the explosion and saw the rescue teams trying to pull out the wounded,” he said.

There were “people still alive under the rubble, and lots of body parts on the ground.”

Rescue personnel were seen directing bulldozers to clear rubble from a road.

Separately, a car rigged with explosives blew up in the Syrian capital killing one person, state media said, blaming unidentified “terrorists” for the latest blast in Damascus.

“One civilian was killed and five others injured in an explosion in the area of Nahr Aisha in Damascus,” state news agency SANA said.

“Investigations showed that terrorists planted an explosive device inside the car, killing the driver,” it said, using the regime’s designation for both rebels and militants.

Five people in the vicinity were wounded and taken to hospital, it said.

Pro-regime newspaper Al Watan however earlier quoted sources as saying that “a vehicle carrying petroleum products caught fire, causing them to explode.”

On Tuesday, regime shelling killed seven civilians, including four children, in the town of Khan Sheikhun.

The toll was confirmed by Syrian civil defence workers, who said 12 others were wounded.

Regime ally Russia and rebel-backer Turkey in September inked a buffer zone deal to prevent a massive regime offensive on the Idlib region, near the Turkish border.

Increased regime shelling on Khan Sheikhun has sparked one of the largest waves of displacement since the truce agreement was struck in the Russian resort of Sochi. Increased regime shelling on Khan Sheikhun has sparked one of the largest waves of displacement since the September deal.

The Idlib region is under the administrative control of Hayat Tahrir Al Sham (HTS), which is dominated by a faction previously known as Al Nusra Front before renouncing its ties to Al Qaeda.

The Turkestan Islamic Party, a group of foreign militants from the ethnic Uighur Muslim minority, also has a large presence in Jisr Al Shughur.

The Daesh militant group has sleeper cells in the wider Idlib region.

Idlib has since September been protected from a massive regime offensive by a fragile ceasefire deal signed by Damascus ally Russia and rebel backer Turkey.

But the region of some three million people has come under increasing bombardment since HTS took full control of it in January.

The capital has been in the grip of a fuel crisis in recent weeks that has seen long queues form outside petrol stations.

Regime forces last year expelled opposition fighters and jihadists from areas surrounding the capital, after years of sporadic rebel rocket fire on Damascus.

Tens of thousands of people were evacuated from the former rebel stronghold of Eastern Ghouta on the capital’s doorstep after a deadly Russia-backed bombing campaign and a string of surrender deals.

Agencies