At least ten airstrikes hit the Syrian city of Idlib overnight Monday, killing 23 people, according to a rights monitor.
The London-based Syrian Observatory for Human Rights said Russian warplanes targeted civilian areas around the city's national hospital and other neighborhoods held by a coalition of rebel groups, including the al-Qaeda affiliate and US designated terrorist group Nusra Front.
"The air strikes are the most intensive on Idlib since the beginning of the truce," Observatory Director Rami Abdel Rahman told AFP news agency. "Even though Idlib is not covered by the truce, it had been relatively calm with only intermittent raids."
In retaliation for the raids, the coalition in control of Idlib, the Nusra-led Army of Conquest, shelled the nearby towns of Foua and Kefraya, which are seen as pro-regime, according to the Associated Press.
Russia on Tuesday denied its planes had conducted any airstrikes against Idlib.
"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.
The Turkish foreign ministry said the strikes had killed more than 60 civilians and complained in a statement about what it said were the "indefensible" crimes of the Russian and Syrian governments.
The Syrian White Helmets — a civil defense organization the rescues civilians — also said dozens of people had been killed in the strikes, and posted a video of a young boy being rescued on its Twitter feed.
Russia's Konashenkov called the Observatory's allegations "a horror story" of the kind he said it had disseminated in the past and said such pronouncements should be regarded with greater skepticism.
Further north, in Aleppo Province, rebel factions backed by the US and Turkey pushed back an Islamic State offensive that threatened a key rebel supply route from Turkey, retaking two towns the jihadist group had captured over the weekend.