Dujarric added that while the investigation, led by Nigeria's Lieutenant General Chikadibia Obiakor, concerns "life and death situations," the findings would not be "for public release."
He did not make clear whether the investigators would point the finger of blame for the attacks, stressing that it is not a judicial body or criminal investigation.
Dujarric said the board will engage with Syria, Russia and Turkey and that he hopes investigators "will have access to the sites of the incidents."
More than 1,000 civilians have been killed in Syria's Idlib region in the four months since Syrian government forces and Russia launched a massive offensive on the opposition-held province, the UN rights chief said last week.
Airstrikes have repeatedly hit hospitals and other buildings housing civilians in Idlib.
On April 30, the Syrian government, supported by Russian air power, began a military offensive against rebels in the provinces of Hama and Idlib, forcing thousands of people to flee.
A ceasefire in the region collapsed in August.
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