US forces are accused of killing at least 40 civilians by bombing a Syrian mosque which their intelligence believed was hosting an Al Qaeda meeting.

The airstrikes allegedly hit a well-known western Aleppo mosque full of hundreds of worshipers on March 16 and injured dozens, Syria said.

The first bomb hit the mosque during prayers before a second blast hit survivors outside, according to a Human Rights Watch report.

US forces are accused of killing at least 40 civilians by dropping a bomb on a Syrian mosque which they reportedly believed was an Al Qaeda meeting. Pictured, volunteers sorting through the rubble after the reported airstrike

The airstrikes allegedly hit a well-known western Aleppo mosque full of hundreds of worshipers on March 16 and injured dozens, Syria said

Syrian civil defence volunteers, known as the White Helmets, dig through the rubble of a mosque in the village of Al-Jineh

Harrowing footage captures a man crying and being restrained by volunteers at the scene of the blast

Others who ran towards the blast to help were also killed, a witness said.

The US claimed the bombings targeted an Al Qaeda meeting hall - but the report claimed there was no evidence that terrorists were meeting there.

The investigation found that the mosque was well known for hosting lectures every Thursday between sunset and evening prayers, CNN reported.

Photos of the building before the attack show it had shelves for shoes and prayer rugs, suggesting that it was a mosque.

Another shot taken after the attack shows a sign that reads 'Saydina Omar ibn Al-Khattab Mosque', according to the report.

The first bomb hit the mosque during prayers before a second blast hit survivors outside, according to a Human Rights Watch report

The US claimed the bombings targeted an Al Qaeda meeting hall - but the report claimed there was no evidence that terrorists were meeting there

The investigation found that the mosque was well known for hosting lectures every Thursday between sunset and evening prayers, CNN reported

US military said an airstrike killed 'several terrorists' at a meeting of senior Al Qaeda terrorists in Idlib in March.

An official told CNN they bombed a building 50 feet from the mosque, and said satellite imagery showed the mosque still standing.

But the Human Rights Watch investigation said US forces got the location wrong - and that it was not in Idlib but the southwest of al-Jinah.

The attack was documented by the Syrian Observatory for Human Rights and the Syria Civil Defense, better known as the White Helmets.

Human Rights Watch interviewed a member of the the Syria Civil Defense, known as the White Helmets, who was at the scene, and four people who were in the building during the strikes.

Photos of the building before the attack show it had shelves for shoes and prayer rugs, suggesting that it was a mosque

Syria Civil Defense workers work tirelessly to try to rescue people from the rubble

Civilians were left in chaos after the blasts. Others who ran towards the blast to help were also killed, a witness said

They collaborated with investigative group Bellingcat, which analyzed footage and photos from the attack, and Forensic Architecture, which created reconstructions of the airstrikes and models of mosque.

'The US seems to have gotten several things fundamentally wrong in this attack, and dozens of civilians paid the price,' Ole Solvang, deputy emergencies director at Human Rights Watch, said in a statement.

'The US authorities need to figure out what went wrong, start doing their homework before they launch attacks, and make sure it doesn't happen again.'

In 2015 US airstrikes killed 42 civilians after hitting a hospital run by Doctors Without Borders in Kunduz, Afghanistan.

It comes after US airstrikes killed 42 civilians after hitting a hospital run by Doctors Without Borders in Kunduz, Afghanistan in 2015

A Doctors Without Borders employee walks inside the charred remains of the organization's hospital after the bombing

It comes amid reports that Islamic State is talking to Al Qaeda about a potential alliance to form a combined terror group as Iraqi troops close in on jihadis in Mosul.

Messengers representing ISIS' leader Abu Bakr al Baghdadi and his al Qaeda counterpart Ayman al Zawahiri have discussed what is understood to be a potential merger deal.

This month it was reported the two terror groups had already formed a partnership in Libya amid mounting pressure on the jihadi movements and a leaked memo suggested they could be working together as one organisation by 2021.

Iraqi Vice President Ayad Allawi revealed the new information in an interview on Monday, citing regional contacts in the country.

'The discussion has started now,' Allawi said.

'There are discussions and dialogue between messengers representing Baghdadi and representing Zawahiri.'

Islamic State split from al Qaeda in 2014 and the two groups have since waged an bitter battle for recruits, funding and the mantle of global jihad.