Russia has angrily denied its planes had conducted air strikes overnight against the Syrian rebel-held city of Idlib, which the Syrian Observatory for Human Rights said had killed 23 people.
"Russian planes did not carry out any combat missions, to say nothing of any air strikes, in the province of Idlib," Igor Konashenkov, a Russian Defence Ministry spokesman, said in a statement on Tuesday.
Turkey said on Tuesday the heavy air strikes reported to have been carried out by Russian jets on a hospital and a mosque in Syria's rebel-held city of Idlib had killed more than 60 civilians and injured around 200 people.
In an emailed statement, the Turkish foreign ministry called on the international community to act swiftly against what it called the "indefensible" crimes of the Russian and Syrian administration.
The Observatory said the air strikes targeted a number of positions in the city, one of them next to a hospital. Seven children were among the dead, Observatory director Rami Abdulrahman said.
Rescue workers in Idlib worked through the night searching for casualties, finding some survivors including a child under the rubble of destroyed buildings, the Civil Defence in Idlib said on its Facebook page.
Idlib city and the province by the same name is a stronghold of rebel groups including the al-Qaeda-linked Nusra Front.
The Russian air force deployed to Syria last year to support President Bashar al-Assad in the war with rebels seeking to end his rule.