At least 42 individuals have lost their lives in a US airstrike that is said to have targeted a mosque full of people in a village west of the Syrian city of Aleppo.

More than 100 people were also wounded in the air raid on the site in the village of al-Jineh, just over 30 km west of Aleppo, the so-called Syrian Observatory for Human Rights said on Friday.

The head of the London-based Observatory Rami Abdel Rahman said the raid targeted the mosque during evening prayers.

The US military confirmed the airstrike early after information emerged about it and said it would investigate reports of civilian casualties. Later in the day, however, the Pentagon denied that a mosque had been hit. It said instead that the airstrike targeted “dozens” of al-Qaeda militants in a building adjacent to the mosque.

“The mosque is still standing and relatively unscathed,” said a spokesman for the Pentagon, which also released an aerial image captured following the attack and showing one flattened building next to another one apparently undamaged.

That assertion, however, has been open to doubt given a series of claims by people in the village and the information released by the Observatory.

The monitoring group also said that many people had been trapped under the collapsed mosque as rescue workers struggled to pull survivors from rubble, and dozens of residents had still been unaccounted for.

Jineh is in the western Aleppo countryside, which along with Idlib is home to hundreds of thousands of Syrians displaced by fighting in other areas. But there are al-Qaeda members and other terrorists from other groups in the area as well.

Abu Muhammed, a village resident, told AFP he heard powerful explosions when the mosque was hit. "It was right after the prayer at a time where there are usually religious lessons for men in it,” he said.

“I saw 15 bodies and lots of body parts in the debris when I arrived. We couldn’t even recognize some of the bodies,” he added.

The US-led coalition has been conducting airstrikes against what are said to be Daesh terrorists inside Syria since September 2014 without any authorization from the Damascus government or a UN mandate. It has alo been involved in a similar campaign in neighboring Iraq.

The alliance has on many occasions attacked Syrian civilians, military and infrastructure under the guise of fighting the terror group.

Syrians dig through the rubble of a mosque following a US airstrike on a mosque in the village of al-Jineh in Aleppo Province on March 16, 2017. (Photo by AFP)

There are also reports that the US-led attacks have on numerous occasions hampered counterterrorism operations by Syrian armed forces.

The latest US air raid came just after Syria contacted the United Nations to warn against an imminent disaster in the wake of air raids by the US-led military coalition close to the Euphrates and Tishrin dams.

Damascus urged UN Secretary General Antonio Guterres to help stop the attacks, “The total destruction of these dams that are being targeted by the airstrikes will wash away and flood cities, towns and villages, endangering the lives of hundreds of thousands of people living in those areas.”

Washington has currently between 800 and 900 Special Operations troops in Syria. A Pentagon official told AFP on Wednesday that the United States is set to deploy about 1,000 additional troops to the northern parts of the country.

In an interview with Chinese TV station Phoenix, Syrian President Bashar al-Assad called the US troops in Syria invaders because under international law foreign governments cannot deploy troops to sovereign countries.

“Any foreign troops coming to Syria without our invitation... are invaders,” said the Syrian leader.

The bloody US attack comes amid a countrywide ceasefire in Syria in parallel with a diplomatic process aimed at ending the crisis in the Arab state.