BEIRUT: Air strikes by Damascus regime ally Russia killed 78 Turkey-backed rebels in northwestern Syria on Monday, a monitor said, in the bloodiest surge in violence since a truce almost eight months ago.

More than 90 others were wounded when Russian warplanes targeted a training camp of the Faylaq al-Sham faction in the Jabal Duwayli area in Idlib province, said the Syrian Observatory for Human Rights.

In early March, a truce brokered between Moscow and Ankara stemmed a Russia-backed regime military offensive on the country's last major rebel stronghold in Idlib.

That onslaught from December had killed more than 500 civilians and displaced almost a million people from their homes in one of the worst humanitarian crises of the nine-year civil war.