The death toll from overnight air raids on the Syrian city of Idlib, apparently carried out by Russian forces, has risen to 23 including seven children, a monitoring group said on Tuesday.
The strikes on the north-western city, which is held by a coalition of mostly hardline Islamist rebel factions including al-Qaeda fighters, come five days after Moscow said it was suspending its strikes on Syrian "gunmen."
The Russian Defence Ministry had said the pause was to allow groups who signed up for a US- and Russian-backed cessation of hostilities a chance to cut their links with the al-Nusra Front, the powerful Syrian branch of al-Qaeda.
Rebels have accused Russia of repeatedly targeting more moderate groups, while the United States has said that battlefield alliances between al-Nusra and other rebels have complicated implementation of the truce, especially around the key northern city of Aleppo.
Ten overnight strikes in Idlib hit areas around the National Hospital and other parts of the city centre, according to Rami Abdul-Rahman, head of the Syrian Observatory for Human Rights.
A volunteer with the White Helmets civil defence group confirmed that the strikes appeared to have been carried out by Russian aircraft.
Rescue workers were searching for survivors under the rubble of the bombed buildings, the volunteer, who asked to be known only as Majed, told dpa.
The Syrian conflict, which began with peaceful protests in March 2011, has spiralled into a multi-sided civil war with a death toll of some 250,000 and half the country's population displaced, according to UN estimates.