A Syrian rescue service said 33 people, mostly women and children, were affected by the gas, which they suspect was chlorine, on Tuesday.
Russian air raids started in Northern Syria after Moscow said one of its helicopters had been shot down, reportedly killing all five crew members.
Kremlin says aircraft shot down while returning to a Russian airbase after delivering humanitarian goods to Aleppo.
The Britain-based Syrian Observatory for Human Rights monitoring group said the hospital strike killed a pharmacist.
Advances in the last day secured key areas inside Manbij, near the Turkish border, a monitor said on Sunday.
Brig. Gen. Mohammad-Reza Naghdi, who heads the Basij paramilitary group, survived an assassination attempt by Israel or rebel forces, Arab news outlets reported over the weekend.
The Syrian group's rebranding could allow it to take part in the negotiations over the country's future, while opening a stream of Qatari and Saudi funds. Now, even the U.S. may see it as a partner.
According to the Fars news agency, Israel fired two missiles at the commander's convoy.
Nusra Front renames itself Jabhat Fatah al Sham so international community can no longer use pretext of its affiliation with Al-Qaida to attack Syrians, group's leader says.
Assad, meanwhile, issued a decree offering an amnesty to armed opposition fighters who surrender within three months and urging all detainees to be freed.