Beirut: At least 57 Syrians were killed after an American airstrike struck a mosque in a rebel-held village on the provincial border between Idlib and Aleppo on Thursday evening. 100 more were injured and the death toll is expected to rise overnight, local activists said. Another report puts the death toll at around 75 already.

Reports quoting eyewitnesses said that the USinfo-icon warplanes bombed a mosque full of worshipers overnight in village of al-Jineh, just over 30 km west of Aleppo, Syrian Observatory for Human Rightsinfo-icon said on Friday.

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

The US military confirmed that it had carried out a deadly airstrike in northern Syriainfo-icon and would investigate reports that civilians were killed when a mosque was struck in the raid.

The observatory said many people were still trapped under the collapsed mosque as rescue workers struggled to pull survivors from rubble, and dozens of residents were still 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.

Abu Muhammed, a village resident, told AFP that 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."

"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 Iraqinfo-icon.

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

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 Nationsinfo-icon 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 Statesinfo-icon is set to deploy about 1,000 additional troops to the northern parts of the country.

In an interviewinfo-icon with Chinese TVinfo-icon 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.