UN Secretary-General Antonio Guterres announced that the United Nations would investigate the attacks in early August, following the UN Security Council pushing for an inquiry.
"The commission is investigating seven incidents of [airstrikes on facilities] in northwest Syria, of which three are in Idlib [province]", the sources said.
A source specified that the airstrikes in Idlib dealt with an attack on humanitarian sites like hospitals and health centres, which had been included on a deconfliction list and shared with the warring parties in order to protect the sites and civilians.
In mid-October, the UN said it would deliver the report about its findings in three months, but would not publish them.
The Russian Foreign Ministry has described the UN probe as provocative in nature, saying that it was promoted by countries that are hostile to the Syrian government and the joint counterterrorism efforts it has undertaken with Russia.
The inquiry was requested by 10 UN Security Council member states — Belgium, France, Germany, the Dominican Republic, Indonesia, Kuwait, Peru, Poland, the United Kingdom and the United States.