A number of people have been killed after airstrikes hit three hospitals in northern Syria, doctors and witnesses say.
According to Medecins Sans Frontieres (MSF), seven people died in an attack in Maarat al-Numan. Activists said another hospital in the town was also hit.
Another strike in Azaz near the Turkish border killed 10, reports said.
MSF blamed pro-Syrian government forces for the raid in on its hospital; Turkey blamed Russia for the Azaz strike.
They come days after Russia and other world powers agreed to a limited cessation of hostilities in Syria.
Almost five years of civil war in Syria have led to the deaths of more than 250,000 people. More than 11 million people have been displaced.
It has not been confirmed who carried out the latest attacks.
However, Mego Terzian, president of MSF France, said the Maarat al-Numan strikes were carried out by forces “loyal to President Bashar al-Assad”.
Mego Terzian told Reuters: “There were at least seven deaths among the personnel and the patients, and at least eight MSF personnel have disappeared, and we don’t know if they are alive.”
Turkish PM Ahmet Davutoglu said a Russian ballistic missile had hit buildings in Azaz, with children among the dead.
Associated Press reported that five people had died at a children’s hospital.
One doctor, Juma Rahal, told the Reuters news agency: “We have been moving scores of screaming children from the hospital.”
Several more people were killed in an air raid on a nearby village, AP reported.
Russia has been carrying out air strikes in Syria since September in support of President Assad and against what it terms “terrorists”.
Azaz has seen an influx of thousands of people fleeing advances by the Russian-backed Syrian army in Aleppo province.
The Kurdish YPG militia, which has been making advances in the area, has also targeted Azaz.
Turkey has shelled Kurdish positions since the weekend and on February 15 promised the “harshest reaction” if the forces tried to take Azaz.
Turkey views the YPG militia in Syria as allied to the outlawed PKK, which has carried out a decades-long campaign for Kurdish autonomy within Turkey.
Syria said the Turkish shelling was a violation of its sovereignty and has called on the UN Security Council to act.
MSF said four rockets had hit the hospital in Maarat al-Numan, a rebel-held town about 20 miles south of the city of Idlib, within minutes of each other on February 15.
The Syrian Observatory for Human Rights, a UK-based group which relies on a network of sources on the ground, said nine people were killed, including a child. The raid also left dozens of others wounded, it added.
MSF’s head of mission in Syria, Massimiliano Rebaudengo, said the strikes appeared to be a “deliberate attack on a health structure”, warning the attack left tens of thousands without medical care.
Another hospital in Maarat al-Numan was also hit, opposition group the Local Co-ordination Committees said, killing three people.
Two rival Syrian rebel groups in the northern town of Azaz have agreed a ceasefire.
The Islamic State in Iraq and Syria (ISIS), linked to al-Qaeda, seized the town on Wednesday from the larger Western-backed Free Syrian Army (FSA).
Fighting between rebel groups has raised fears of a war within a war.
The clashes come ahead of a deadline, on Saturday, for Syria to provide a list of its chemical weapons facilities as part of a US-Russian deal for the country to destroy its deadly arsenal.
Russia’s Deputy Foreign Minister, Sergei Ryabkov, is currently holding talks in Damascus about the deal.
But the agreement still faces many hurdles – including the differing opinions of the US and Russia.
US Secretary of State John Kerry said a “definitive” UN report had proved that the Syrian government was behind a deadly chemical weapons attack in the Damascus suburbs of Ghouta on August 21.
But Damascus – backed by Moscow – insists that rebel forces carried out the attack.
The West also wants any UN resolution on Syria’s chemical weapons to include the threat of military force in the result of non-compliance – but Russia objects to any mention of this.
Syria’s President Bashar al-Assad, in an interview with Fox News, said it could take about a year to destroy Syria’s chemical stockpiles and could cost about $1 billion.
Under the ceasefire deal in Azaz the two rebel sides have agreed to exchange prisoners and hand back property.
Two rival Syrian rebel groups in the northern town of Azaz have agreed a ceasefire
It is unclear whether the ceasefire will have an impact on clashes between the groups elsewhere in the country.
Analysts say there is more chance that the US and other Western powers may arm the Free Syrian Army if it shows a distinct separation from the Islamists.
The fighting in Azaz began when a wounded rebel – either from ISIS or from an allied group, al-Muhajireen – was taken to a field clinic and, while there, he was filmed as part of a fundraising exercise.
The wounded fighter demanded the film, and called some of his friends to come and help him.
Free Syrian Army (FSA) rebels from a unit called the Northern Storm brigade were guarding the field clinic, and there was a confrontation which ended up with ISIS launching a full attack on the town, pushing out the Northern Storm brigade.
ISIS is reported to have made a number of arrests of activists, journalists and even Sharia court officials during the time it controlled Azaz.
One eyewitness inside the town said no-one was smoking on the streets – tobacco is forbidden according to strict Islamist doctrine.
While the Azaz violence seems to have been the result of a particular set of circumstances rather than a long-planned offensive, our correspondent says there is a record of skirmishes between the Jihadis and FSA brigades for control of the border crossings into Turkey.
Meanwhile, the party of Syria’s Deputy Prime Minister Qadri Jamil insists he was misquoted in Friday’s edition of the UK’s Guardian newspaper.
Qadri Jamil reportedly told the paper that the civil war had reached stalemate, with neither government forces nor the rebels strong enough to win – and that the government would use proposed talks in Geneva to call for a ceasefire.
But the People’s Will Party said the Guardian journalist was ”neither precise nor professional” about what he quoted Qadri Jamil as saying.
Iranian President Hassan Rouhani has said Tehran is ready to help broker peace in Syria, as part of what he called his country’s “constructive engagement” policy with other nations.
In an article in the Washington Post newspaper, Hassan Rouhani wrote: “We must create an atmosphere where peoples of the region can decide their own fates.”
Correspondents say the article is the latest signal that Hassan Rouhani wants to improve Iran’s relationship with the US and other countries that believe Iran is developing nuclear weapons.