UOSSM also said that another 400 people had been injured in the town of Khan Sheikhoun.
People choked or fainted after the attack, while video footage showed some foaming at the mouth, said the Syrian Observatory for Human Rights.
Other videos, many of which show distressing images, showed people gasping for air and children being given oxygen.
According to reports, just hours after the attacks a small field hospital in the region was partly destroyed by airstrikes.
The Syrian Coalition - an opposition group also based outside the country - said planes from President Bashar al Assad's military were to blame.
****
An all-out strike by workers at the embattled company over proposed cost-cutting measures is well into its second week.
The strike and picketing will continue during the talks.
Bus Éireann will also be attending the talks, stating: "The company’s financial situation continues to deteriorate. Achieving savings to remain solvent and sustain the business is now vital.”
The National Bus and Rail Union (NBRU) says the first item on their agenda when talks get underway tomorrow morning will be a "complete review of the managerial structure at Bus Éireann".
****
Tim Amstrong, who heads up Verizon's AOL division, took to Twitter on Monday to welcome "Oath" to the world.
Verizon is set to complete its $4.48 billion purchase of Yahoo's internet assets by the end of June. From that point on, Oath will be the primary name you see connected with Verizon's digital media division, representing its family of digital content services.
The company is not, however, killing off the old brands completely.
****
The first, youth-targeted outlet arrives in Dundrum Town Centre later this month, with a further Irish store to open in time for summer and advanced talks underway to add between two and three before Christmas.
Owned by Australian billionaire Solomon Lew's Premier Investments, Smiggle's move into Ireland will represent its first entry into the euro zone.

****
Linking Germany and Switzerland, the eight-minute flight over Lake Constance from St Gallen-Altenrhein in Switzerland to Friedrichshafen in southern Germany takes off for the last time on April 14th.
The route was launched by the Austrian People’s Air Group in November 2016, offering twice-daily flights each way across the 20-km distance. A one-way ticket between the two airports was priced at €40.
“The withdrawal of the flight is very regrettable to the region and the Bodensee Airport,” said airport boss Claus-Dieter Wehr.