"There were at least 15 dead among the ranks of Jaish al-Islam and 23 among its adversaries" as well as two civilians, the Britain-based Observatory said.
Another 70 were wounded.
Jaish al-Islam said its opponents had provoked the clashes by harassing reinforcements headed for Qabun, east of the Syrian capital, a front with regime forces.
Faylaq al-Rahman denied the allegation.
In May 2016, more than 300 people were killed in a battle between the two sides.
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Another 70 were wounded.
Jaish al-Islam said its opponents had provoked the clashes by harassing reinforcements headed for Qabun, east of the Syrian capital, a front with regime forces.
Faylaq al-Rahman denied the allegation.
In May 2016, more than 300 people were killed in a battle between the two sides.
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