When they exploded, "they created a large gas cloud. The explosion led to 42 cases of choking accompanied by severe allergic reactions and severe vomiting," a statement said.
The coalition urged an international investigation into the alleged attack.
UN chief Ban Ki-moon has called on Damascus to approve a UN mission of inspectors to probe the alleged use of chemical weapons in the spiralling conflict that erupted in March 2011.
But Zohbi said Syria could not trust UN inspectors from Britain and the United States.
"We also do not trust their qualifications. Their aim is to juggle with facts," he told Russia Today, although Syria would accept Russian inspectors.
"We won't mind if Russians would be among the experts; quite the contrary, we only welcome this idea. We are quite sure in their high qualification and ability to clearly see into such matters," he was quoted as saying.
Along with China, Russia has blocked several UN Security Council draft resolutions threatening sanctions against President Bashar al-Assad's regime.
US President Barack Obama warned Syria on Friday that using chemical weapons would be a "game changer", after the US, Israel and Britain cited signs that Assad's regime has used the deadly agent sarin.
But Obama said Washington must act prudently and establish exactly if, how and when such arms may have been used, promising a "vigorous" US and international probe into the latest reports.
Russia warned against using these reports for military intervention.
"We must check the information immediately and in conformity with international criteria, and not use it to achieve other objectives. It must not be a pretext for an intervention in Syria," deputy foreign minister and Middle East envoy Mikhail Bogdanov said in Beirut.
Zohbi linked the chemical arms accusations to what he said were "qualitative changes on the battlefields" to the advantage of regime forces, RIA Novosti news agency reported.
On Friday he said at a news conference in comments published by the Interfax news agency that chemical weapons were used by rebels and originated in Turkey.
The Syrian opposition has stepped up pressure by urging the UN Security Council to take immediate steps, possibly even by imposing a no-fly zone on Syria.
British Prime Minister David Cameron said the growing evidence that Assad had turned chemical agents on his own people was "extremely serious".
Fighting continued unabated on Saturday, with at least 32 people killed nationwide, including 10 in shelling on Douma northeast of Damascus, the Syrian Observatory for Human Rights said.
The watchdog also reported that rebels seized the Handarat Palestinian refugee camp on the northern fringes of Aleppo after months of fierce fighting.
Analysts said Syria's neighbours face a growing risk of the conflict spilling across the region as Assad turns to ever more desperate acts to halt rebels.
They said Lebanon and Jordan will be the most vulnerable, while Iraq could also be affected along with Israel and Turkey.
"It is a very vulnerable region and there is a risk of escalation," said Anthony Skinner of British risk consultancy Maplecroft.
Iraqi Prime Minister Nuri al-Maliki, alluding to Syria, said sectarian strife growing in his own country "came back to Iraq because it began in another place in this region."
Senior Egyptian officials, meanwhile, visited Iran to further a Cairo proposal for an Islamic quartet of Egypt, Turkey, Saudi Arabia and Iran to help resolve the Syrian conflict, the Egyptian presidency said.
Cairo, Ankara and Riyadh support the mostly Sunni rebels in Syria, while Shiite Iran backs Assad's minority-led Alawite regime.