At least 33 people killed in coalition strike on school used as refugee centre near jihadi-held town in northern province of Raqqa, says monitor

An airstrike by the US-led coalition against Islamic State on a school west of the Syrian city of Raqqa has killed at least 33 people, many of whom had fled nearby fighting, sparking further concerns that new rules of engagements may be causing an increase in civilian casualties.

The attack follows a separate US strike on a mosque complex in the north-west of the country last Saturday that killed at least 52 people. The incident triggered fears that a White House-ordered review of rules governing the use of drones had already given military planners more flexibility on ordering strikes.

Activists in Syria said the attack on the school took place in the same area where US-backed Kurdish forces had begun an operation on Wednesday to separate the town of Tabqa from Isis’s last urban stronghold in Syria.

“There were only two survivors from this,” said one witness. “And they have still been buried. Most of these people, maybe all of them, had taken shelter in this building from the fighting and the planes. They were hiding for their lives.”

Donald Trump has pledged to ease restrictions on how and when US drones can be used and signalled a tougher approach to targeting Isis and al-Qada franchises in northern Syria.

As US troops and their proxies began an offensive west of Raqqa, fears mounted that the new posture had led to fewer restrictions on what could be targeted in active war zones, such as Syria and Iraq.

“There has not been a decree to that effect yet,” said a senior regional military source. “But there has been a definite change in mood. Often that is all it takes.”

If approved, the changes being sought by Trump would mean the Pentagon could approve attacks without presidential consent and the threshold of “near certainty” that there be no civilian deaths would be open to potentially looser interpretation.

The US military has acknowledged that warplanes flown under the coalition banner were active in the area on Tuesday and pledged to investigate whether civilians were among those killed. It also admitted to carrying out the strike in Idlib, which it said targeted an al-Qaida planning meeting, but denied that the building hit had been a mosque.

Images from the site and witness accounts confirmed the targeted building had been part of a mosque compound.

Over the past eight months, there have been four cases in which US planes or drones have been blamed for mass civilian casualties in Syria. The first strike occurred last July near the town of Manbij, which, at the time, was being recaptured from Isis. Up to 150 civilians are thought to have died in the attack, the single deadliest strike since late 2014.

Since then, up to 3,500 civilians have been killed in the north of the country by a Russian and Syrian air campaign.

The US has conducted nearly 3,000 airstrikes against Isis targets in northern Syria, with thousands more in Iraq in support of national forces.

Barack Obama defined the US role as partnering with local militaries and proxies and acting in support of them. President Trump appears to have given his commanders more latitude to take leading roles.

The defence secretary, Jim Mattis, a former commander of the US Marine Corps, ordered 500 marines to be deployed north of Syria to provide artillery fire in support of an eventual ground operation.

In the meantime, Iraqi forces, backed by US airstrikes continue to press into a pivotal neighbourhood of the Iraqi city of Mosul. By Wednesday night, they were several hundred metres away from the Grand Mosque, where Isis leader Abu Bakr al-Baghdadi, proclaimed himself leader of a caliphate almost three years ago.

At least two-thirds of Mosul has been recaptured from Isis and what remains of the organisation there has been confined to the north-west of the city. Nearly six months into the war to reclaim Iraq’s second biggest city, there are growing hopes that the battle may be finished before the onset of summer, allowing focus to be switched to Raqqa – potentially the last major battle fought against Isis.

“We are getting there now,” said an Iraqi colonel whose troops were supporting the push on the Grand Mosque. “Every yard they have had to fight for and I know they have surprises waiting. Any civilian that can get out, we are grateful for.

“The conditions there are very tough. We are trying to do everything we can to protect them. But Isis are not.”