Some 50 militants with the al-Qaida-linked Nusra Front were killed in an explosion in Syrian city of Idlib, media reports said.
On Sunday, the cars, loaded with ammunition, went off near a gathering of Nusra militants, with no further information indicating whether the bombings were planned or accidental, Xinhua news agency reported.
The cars belong to the rival Ahrar al-Sham movement, which lost dominance of Idlib earlier in the day to the Nusra Front, or the Front for Liberating the Levant, following infighting between both groups.
Their infighting has recently flared in Idlib, which is largely under the Nusra's control, with Ahrar al-Sham's reported withdrawal from the city, pan-Arab Mayadeen TV reported.
The Nusra Front is designated as a terror group by the international community and the UN, and was excluded from any deal along with the Islamic State group.
The battles against Nusra have pushed several rebel groups previously allied with it to withdraw amid reports that Ahrar al-Sham has joined the alliance with the Turkey-backed Free Syrian Army.