At least 46 people have been killed and more than 100 injured in overnight strikes by unidentified jets on a mosque in northern Syria, a monitoring group said on Friday.

Many of the people killed in the bombing in the village of al-Jinneh in the western part of Aleppo were civilians, the Syrian Observatory for Human Rights added.

The volunteer rescue group, White Helmets, said its teams were searching the wreckage for survivors.

Activist Mohammed al-Shaghel, who visited the bombed site, said aircraft, believed to be from a US-led coalition, targeted the mosque.

"The mosque was flattened by the raid," he posted in a WhatsApp message.

Other activists posted online pictures of what they claimed were remains of a US-made missile allegedly weighing 52 kilograms at the site.

"We surely know that the planes were not Russians nor regime planes," Rami Abdel Rahman, head of the Britain-based Syrian Observatory for Human Rights, told dpa.

US Central Command (Centcom) said its forces had conducted an airstrike on a meeting of al-Qaeda meetings on Thursday in the vicinity of Idlib in north-western Syria.

"We take every precaution to prevent and mitigate civilian casualties, so we take every allegation seriously," Andy Stephens, the Centcom Media Operations Officer, told dpa by mail.

The US military had earlier said it had killed a number of extremists in an airstrike in Syria, but denied it was responsible for the bombing of a mosque there.

The US-led coalition has been bombing jihadist groups in war-torn Syria since 2014.

Russia, a key military ally of Damascus, has been mounting a separate air campaign in Syria since September 2015.

Turkey's deputy premier, Noman Kurtulmus, denounced Thursday's airstrike as a "crime against humanity and a war crime."

He did not say who was behind the bombing.

But, Abdulkafi Alhamdo, an activist based in Aleppo, explicitly blamed the US administration for the strike.

"[US President Donald] Trump is targeting mosques. It is not strange that this person, who always shows hatred to Muslims, targets their mosques? Would the world keep silent if this was a church?" Alhamdo said in a post on social media.

The al-Qaeda-linked Jabhat Fatah al-Sham and its rival Islamic State are excluded from a Russian-Turkish brokered ceasefire that took effect in Syria late last year.

Each group has since taken credit for a series of deadly attacks inside Syria.

The death toll in a suicide bombing inside a court complex in Damascus on Wednesday has risen to 45 people, the Observatory reported on Friday.

The fatalities included 38 civilians, the watchdog added.

So far, there has been no claim of responsibility for the attack.