Their ambulance was completely destroyed in the Ma'arat Humeh area in southern Idlib province on Wednesday, said Stephane Dujarric, spokesman for UN Secretary-General Antonio Guterres.
"The UN continues to call on all parties to the conflict to respect and protect medical and humanitarian personnel, their means of transport and equipment and property, as well as hospitals and other medical facilities, in accordance with international humanitarian law," Dujarric said.
As the fighting continues in the northwest, the spokesman also said explosive hazards continue to exact a heavy toll on the civilian population across Syria.
"The threat of explosive hazards remains a major concern, with over 10 million people estimated to live in contaminated areas," he said.
Dujarric said the attack prompted Mark Cutts, the UN's deputy regional humanitarian coordinator for the Syria crisis, to condemn it and all attacks on civilians and civilian objects.
"Since the end of April, there have been at least 42 attacks on healthcare (entities) reported, affecting 36 health facilities and seven ambulances," he said. "At least 17 health workers and patients have been killed."
"More than 500 civilian deaths have been documented by the United Nations over the past three and a half months in northwest Syria," Cutts added, noting that most of these deaths have been the result of the relentless campaign of airstrikes by the Syrian Government and its allies.
The coordinator also said that Wednesday's attack highlights the horror of what's going on in Idlib and northern Hama governorates, where 3 million civilians remain trapped and where humanitarians, medical staff and rescue workers continue to pay with their lives in their efforts to help others.