Air strikes on Al-Qaeda's former affiliate in Syria on Tuesday killed 26 people in the country's northwest, most of them civilians, a monitoring group said.
The headquarters of Fateh al-Sham Front and the surrounding neighbourhood in Idlib city were battered by at least 10 strikes at dawn, said the Syrian Observatory for Human Rights, which relies on a network of sources on the ground for its reports.
Observatory head Rami Abdel Rahman initially said there were only 10 civilians among the dead.
But after further verification, he said the victims included "16 civilians, most of them women and children".
"The toll could rise because some people are trapped under the rubble and unaccounted for," he said.
Abdel Rahman said the raids were likely carried out by Russian warplanes -- allied with Syria's government -- or by a US-backed air coalition.
But Russia quickly denied it had struck Idlib.
"Russian military planes did not carry out a single strike in Idlib yesterday, or this week, or even since the beginning of 2017," its defence ministry said in a statement.
"Any information on these strikes are well-known lies."
Moscow has waged a fierce bombing campaign in support of the Damascus regime since September 2015, a year after the US-led coalition began its own strikes against Islamist militant groups.
Fateh al-Sham has come under increasing pressure in recent weeks in Idlib province, the only remaining opposition-held province in war-ravaged Syria.
Bombing raids against the group have escalated, including one US strike in January that killed more than 100 fighters at a training camp in Idlib province.
The US-led coalition has mostly focused on Fateh al-Sham's Islamist militant rival, the Islamic State(IS) militant group, but it has also hit operatives from other factions.
Rebel groups have held Idlib province since the spring of 2015, four years after conflict first broke out.
More than 310,000 people have died since, and millions have been forced to flee their homes.
