"Russia's attack on the training centre of the Syrian national army forces in the Idlib region shows it does not want lasting peace in the region," Erdogan said in a televised address.

A Russian war plane on Monday hit a training centre for Turkish-backed fighters in the northwestern Syrian province near Turkish border.

The Britain-based Syrian Observatory for Human Rights said the attack killed 78 fighters in the bloodiest surge in violence since a truce almost eight months ago.

The pro-Ankara group, known as Faylaq al-Sham, retaliated by killing at least 15 Moscow-backed fighters, the monitor said.

Faylaq al-Sham is a Sunni Islamist group that has acted as Turkey's proxy during several Turkish military campaigns on Syrian soil, and has also been the source of pro-Ankara mercenaries sent to fight in Libya.

A truce at the start of the year brought an end to a Russia-backed Syria regime offensive that had killed more than 500 civilians and displaced almost one million people.

It was one of the worst humanitarian crises of Syria's nine-year civil war.

The last major rebel stronghold covers around half of Idlib province as well as slivers of adjacent provinces.