The nongovernmental organization is known internationally as Medecins Sans Frontieres, or by the acronym MSF.
"This appears to be a deliberate attack on a health structure and we condemn this attack in the strongest possible terms," said Massimiliano Rebaudengo, MSF's Head of Mission. "The destruction of the hospital leaves the local population of around 40,000 people without access to medical services in an active zone of conflict."
Doctors Without Borders said that the clinic had been struck by four projectiles within a few minutes and subsequently destroyed. It reported at least eight staff members missing. Doctors Without Borders said that there were two series of at least two attacks each. The dead included five patients, one patient caretaker and a hospital guard.
Doctors Without Borders said it had been supporting the hospital since 2015, providing medical supplies and running costs. The hospital had 30 beds, a staff of 54, two operating rooms and an outpatient wing, the organization said.
The Syrian Observatory for Human Rights said that Russian warplanes had targeted the makeshift hospital.
Riyad Haddad, the Syrian ambassador to Russia, said today on Russian state TV that Russia had nothing to do with the airstrike.
"As for the hospital that was destroyed, in reality it was destroyed by the U.S. Air Forces," Haddad said, adding that his theory was backed by intelligence.
The U.S. today denied any involvement in the attack. Col. Steve Warren, a spokesman for the U.S. military in Iraq, told ABC News that the U.S. military was not operating in that area. He said the U.S. only conducted missions in Raqqa and Hassakah.
"The United States condemns airstrikes conducted in and around Aleppo today against innocent civilian targets, including a hospital run by Medecins Sans Frontieres and the Women's and Children's hospital in Azaz city. ... We call again on all parties to cease attacks on civilians and take immediate steps to grant humanitarian access and the cessation of hostilities that the Syrian people desperately need," the U.S. State Department said in a statement.
In October 2015, the U.S. mistakenly attacked a Doctors Without Borders hospital in Kunduz, Afghanistan, killing 30 hospital staff and patients. President Obama apologized to Doctors Without Borders for the airstrike.