More than 40 jihadists killed in north Syria airstrikes

"Aircrafts believed to belong to the US Air Force struck a Fateh al-Sham camp in Jabal al-Sheikh Suleiman, killing around 50 militants and wounding dozens more," a source told The New Arab.

"Similar airstrikes hit the headquarters of Nour al-Din al-Zenki Movement in Aleppo, killing three militants and wounding several others," another source added.

However the Syrian Observatory for Human Rights, which also reported the deaths, said it could not specify who carried out the strikes in the western part of the Aleppo province.

The US-led coalition, as well as the Syrian regime and its ally Russia have carried out strikes against Fateh al-Sham targets in recent weeks.

"Warplanes, which may have been Russian or coalition aircraft, struck a Fateh al-Sham camp in Jabal al-Sheikh Suleiman," the Britain-based Observatory said.

The militant group, formerly known as al-Nusra Front, is not party to a Russian- and Turkish-brokered ceasefire that went into effect on December 30 and has sustained major losses in air strikes in recent weeks.

The former al-Qaeda affiliate is regarded by the UN Security Council as a "terrorist" organisation.

Around 100 of its fighters have been killed since the start of the year, according to the monitor.

Fateh al-Sham is allied with Islamist rebel groups that are party to the ceasefire and together they control virtually all of Idlib province in the northwest as well as parts of Aleppo province.

Their alliance has scuppered previous attempts to broker a ceasefire between the government and non-jihadist rebel groups, with Damascus and its allies citing the Fateh al-Sham presence as grounds for continuing hostilities in areas they control.

Agencies contributed to this report.