The UN Commission of Inquiry on Syria also condemned horrific violations by jihadists and voiced concern that Al-Qaeda-affiliated militants may have recruited hundreds of children into their ranks.
Commission chief Paulo Pinheiro told the UN Human Rights Council that widespread, targeted aerial attacks on hospitals and clinics across Syria "have resulted in scores of civilian deaths, including much-needed medical workers."
"More than 700 doctors and medical personnel have been killed in attacks on hospitals since the beginning of the conflict," he said.
"As civilian casualties mount, the number of medical facilities and staff decreases, limiting even further access to medical care," he said.
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Pinheiro also denounced frequent attacks on other infrastructure essential to civilian life, such as markets, schools and bakeries.
"With each attack, terrorised survivors are left more vulnerable," he said, adding that "schools, hospitals, mosques, water stations ... Are all being turned into rubble."
War broke out after President Bashar al-Assad's regime unleashed a brutal crackdown against protesters demanding political change in Arab Spring-inspired protests.
It has since become a multi-front war between regime forces, jihadists and other groups with the civilian population caught in the crossfire.
The UN and rights groups have repeatedly called on all sides in the war to stop attacking civilian infrastructure including hospitals.
Pinheiro also said the commission was investigating allegations that the Al-Nusra Front "and other Al-Qaeda-affiliated groups have recruited hundreds of children under 15 in Idlib" in northwestern Syria.
Pinheiro also condemned the violations committed by the Islamic State group.
In a report published last week, the commission warned that IS jihadists were continuing to commit genocide against the Yazidi minority in Iraq and Syria.