Air strikes struck a hospital in western Syria last week, killing two people, and there is evidence chemical weapons were used, Medecins Sans Frontieres (MSF) says.
A Syrian military source said this week allegations that government forces were using chemical weapons were "devoid of truth".
MSF said on Friday a bomb dropped from a helicopter hit the entrance of a hospital supported by the medical aid group in the rebel-held town of Latamneh in Hama province on Saturday.
The health authority of opposition-held parts of Hama blamed the attack on Syrian government warplanes. The Syrian government denies attacking hospitals and says it only targets militants.
The medical charity said the strike knocked the hospital out of service for three days, after which the emergency room reopened.
The attack killed an orthopaedic surgeon, leaving nearly 120,000 people with only two such doctors, it added.
Jets have pounded rebel-held areas in rural Hama this week, as government forces fought to reverse the biggest assault by insurgent groups in months.
The Syrian Observatory for Human Rights, a UK-based war monitoring group, said the escalation in strikes injured at least 50 people in recent days.
Air strikes that hit the same town of Latamneh on Thursday also led several people to choke, the Observatory and a doctor had said, describing it as sign of a gas attack.
Abdallah Darwish, head of the health authority for rebel-held areas of Hama province, said earlier the strikes on Thursday caused "irritation, heavy foaming from the mouth and constricting pupils" citing his medical staff on the ground.
A Syrian military source denied the accounts on Thursday.
A joint inquiry for the United Nations and the global chemical weapons watchdog has previously accused government forces of toxic gas attacks. The Syrian government has repeatedly denied using such weapons during the six-year-old war.