At least 105 Turkish-backed fighters have died and almost 90 wounded in airstrikes by Russian warplanes on a rebel training camp in northwestern Syria on Monday, according to the Britain-based Syrian Observatory for Human Rights.

The military training camp is located in the Jabal al-Dawila area in Harem, north-west of Idlib and belongs to the Ankara-backed Faylaq al-Sham Corps, one of the biggest alliance of Sunni Islamist rebels in Syria.

The camp was supposed to graduate a batch of fighters within days, the British war-monitoring group added. Leaders of the camp were among those killed in the airstrikes, said Youssef Hammoud, a spokesperson for the groups, Arab News reported, adding that Syrian rebel groups vowed to retaliate.

Earlier this year Russia and Turkey brokered a truce in Idlib to halt a Damascus-led military offensive against the last rebel enclave in Syria, that has displaced hundreds of thousands.