Medecins Sans Frontieres claims a strike on one of its medical facilities was a deliberate attack by pro-Syrian government forces.
Missiles hit a makeshift Medecins Sans Frontieres hospital in Syria's Idlib province.
The president of Medecins Sans Frontieres France, Dr Mego Terzian, says the strikes kept coming.
Dr Terzian says four missiles hit the facility in Maarat al-Numan within minutes of each other.
He says the dead include medical workers and patients.
"A deliberate attack against medical structure. It's clearly an attack against the medical mission. To be today a doctor or a nurse in the areas controlled by the opposition, it's equal to be a criminal. Unfortunately, if you are a doctor and you are working in a hospital, clearly, you are under attack by the Syrian regime."
It is not the first time the organisation's facilities in Syria have been destroyed in air strikes.
Mr Terzian says, this year, several hospitals supported by Medincins Sans Frontieres in opposition-held areas have been struck by missiles.
"The author of the strike is clearly the Syria-led coalition -- either the government or the Russian planes struck probably the hospital. Unfortunately, it's not the first time. Since early January 2016, five structures, medical structures, supported by my organisation have been bombed in Syria, in three provinces -- in Idlib, in Aleppo and, also, in the south in Deraa."
The air strikes did not end with the Medicins Sans Frontieres facility.
And further north in the town of Azaz, near the Turkish border, a children's hospital and a school sheltering families fleeing the offensive were hit, killing many more people.
The air strikes come days after Russia and other parties in the Syrian war agreed to a limited cessation of hostilities.
Turkish prime minister Ahmet Davutoglu says the strikes confirm Russia's intentions.
"Despite the agreement in Munich, Russia is clearly showing its intention is not to make peace or keep a ceasefire. Russia is ready to kill more civilians and perpetrate more massacres to keep the Syrian regime alive."
Russia insists it is targeting terrorist groups and has denied killing civilians since its air campaign began in September at the request of the Syrian government.
The raids on armed opposition groups are helping the Syrian army advance toward the city of Aleppo, part of a major supply route to civilians and opposition groups in the area.
The High Representative of the European Union for Foreign Affairs and Security Policy, Federica Mogherini, has condemned the most recent air strikes.
"What happened today to the hospital of Medecins Sans Frontieres, is completely unacceptable, and we will continue to pressure all the parties to respect basic principles of humanitarian law and focus on the protection of civilians. In the same spirit, the European Union is taking a fundamental role in the task force that has started already to work in Geneva, in these days, on humanitarian delivery."
But Syrian president Bashar al-Assad says ceasefires are difficult to implement.
"Until now, we hear about them requesting a ceasefire within a week. Okay, then who is capable of bringing together all of these conditions within a week? No-one. Who will speak to the terrorists if a terrorist organisation refuses to adhere to the ceasefire? Who will make them accountable? From a practical perspective, all this is difficult to implement."
Mr Assad says the cessation of operations must be done with the aim of improving security.
In his televised town hall-style address, Mr Assad also aimed criticism at Saudi Arabia and Turkey.
He has played down threats of a ground assault, claiming the two allies would have already attempted to put soldiers on the ground if they were serious.
UN Syrian envoy Staffan de Mistura has arrived in Damascus to follow up the Munich meeting where parties agreed to work toward a cessation to hostilities.
