Air strikes in northern Syria have killed at least 25 members of a prominent jihadist group, including senior figures, monitors say.
The UK-based Syrian Observatory for Human Rights says it is not clear who carried out the attack against the Jabhat Fateh al-Sham group, formerly known as Nusra Front.
Russia and Turkey say the group is not included in a ceasefire deal in Syria.
Meanwhile, rebel groups say they are halting preparations for peace talks.
A statement signed by a number of groups cited "many big breaches" by the Syrian government and its allies as a reason.
The ceasefire was brokered by Turkey and Russia last Thursday and has mostly held since then. Peace talks were planned for later this month in Astana, Kazakhstan.
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The Syrian Observatory said it could not determine if the strikes, in the countryside of Idlib province, were carried out by the US-led coalition or Russia.
Among the dead were leading members of Jabhat Fateh al-Sham, which was holding a meeting there, the Observatory added, without identifying them. Many others were wounded, it said.
Abu Anas al-Shami, a Jabhat Fateh al-Sham spokesman, said in a statement the attacks were carried out by the US-led coalition.
"The headquarters targeted by the international coalition a short time ago are a main headquarters for that area and contains a number branch offices, leading to the killing of the brothers," he said in a statement quoted by Reuters news agency.