At least 23 people, many of them civilians, have been killed in air strikes on a rebel-held city in north-western Syria, activists say.
Several multi-storey buildings in Idlib were levelled in the dawn attacks.
One report said they included the HQ of the al-Qaeda-linked jihadist group, Jabhat Fateh al-Sham (JFS).
It was not clear whether the air strikes were carried out by Syria’s government, its ally Russia, or a US-led coalition that has also bombed JFS.
The Russian defence ministry was swift to deny any involvement, stressing that its warplanes had not carried out any strikes in Idlib so far this year.
- Returning home to ruins of East Aleppo
- Why is there a war in Syria?
The Syrian Observatory for Human Rights, a UK-based monitoring group, reported on its website that there were at least 10 air strikes in Idlib early on Tuesday.
It said the districts of Amn al-Dawla, Amn al-Askari, al-Dabit and Wadi al-Nasim were hit, as well as the al-Jaraa roundabout, the Shuaib mosque and the municipal stadium. Sixteen civilians were among 26 people killed, it added.
The Syria Civil Defence, whose first responders are known as the White Helmets, put the death toll at 23, and noted that people were still searching through the rubble of the destroyed buildings.
One photo posted online by the organisation showed the body of a baby boy found by rescuers; another featured a young girl who it said was pulled out alive.
Later, the Syrian Observatory’s director, Rami Abdul Rahman, was quoted by the AFP news agency as saying one of the buildings had been the headquarters of JFS.
The group, known as al-Nusra Front until it broke off formal ties with al-Qaeda last July, controls Idlib and the surrounding province along with several rebel factions.
The incident was one of the deadliest in Syria since the start of a nationwide cessation of hostilities brokered by Russia and Turkey on 30 December.
The truce does not include JFS and the rival jihadist group, Islamic State (IS), which are both designated as terrorist organisations by the United Nations.
Last month, the US said a strike involving a B-52 bomber and several drones had killed more than 100 militants at a JFS training camp in Idlib province.
Russian warplanes have also frequently targeted a number of towns and villages in the area since September 2015, when Moscow intervened in the civil war.
More than 300,000 people have been killed and 11 million others displaced since an uprising against President Bashar al-Assad began almost six years ago.