At least 14 patients and three doctors have been killed in an air strike on a hospital in the Syrian city of Aleppo, the charity Medecins sans Frontieres (MSF) says.
Among those killed in the MSF-supported al-Quds hospital was one of the city's last paediatricians, MSF said.
Local sources blamed Syrian or Russian war planes. The Syrian military has denied targeting the hospital.
Monitors say attacks by both sides left 34 dead and dozens wounded on Thursday.
Violence in Syria, and particularly in Aleppo, has intensified in recent days, despite a partial truce.
The International Committee of the Red Cross says Aleppo is on the brink of a humanitarian disaster.
The upsurge in violence comes amid reports that the Syrian army, backed by Russian air power, is gearing up for a major offensive on the city.
The escalation has threatened to derail UN-brokered peace talks in Geneva, which resumed last month.
On Wednesday, the UN envoy to Syria urged the US and Russia to intervene "at the highest level" to save the talks.