Dozens killed as rebels clash in northern Syria
Fighting flared on Tuesday between the jihadist-led Hayat Tahrir al-Sham and a rival rebel alliance in the northern province of Aleppo, the Syrian Observatory for Human Rights said.
The fighting then spread to parts of the neighbouring province of Idlib the next day, and then into Hama province on Thursday, the Britain-based monitor said.
"New fronts have opened up," Observatory chief Rami Abdel Rahman said, with HTS seizing more than a dozen areas in recent days.
On Wednesday, 17 HTS fighters and 16 combatants from the Turkish-backed National Liberation Front rebel alliance were killed.
That brought the overall death toll to 75 fighters from both sides, as well as six civilians, according to the Observatory.
HTS had on Monday accused NLF member Nureddine al-Zinki of killing five of its fighters, and launched an offensive against rebel positions.
HTS, which is led by the jihadists of Syria's former Al-Qaeda affiliate, and rival rebels from the NLF have been battling each other for territory for two years.
And the last major rebel bastion of Idlib - which includes adjacent parts of Aleppo and Hama - has been regularly rocked by assassinations.
Since September, the stronghold has been protected from a regime offensive by a shaky deal signed by rebel backer Turkey and government ally Russia to set up a buffer zone around it.
Sparked by the brutal repression of anti-regime protests in 2011, the civil war has since killed more than 360,000 people and displaced more than half the country's population.
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