Twenty-one people have been hospitalised after inhaling gas when their government-controlled village in Syria was shelled by rebels, state media is reporting.
The victims were from the village of al-Rasif in Hama province, SANA news agency said on Sunday, citing a local hospital spokesperson regarding the injuries.
A Syrian military source said that five shells carrying toxic gas were fired by opposition factions at al-Rasif from a rebel-controlled area.
In retaliation to the alleged poisonous attack, the Syrian army destroyed targets in the rebel area, the source told dpa without adding further details.
President Bashar al-Assad's government and the rebels have traded blame for poisonous gas attacks during the course of the country's eight-year conflict.
Meanwhile on Saturday, US-backed forces proclaimed the capture of Islamic State's last territory in Syria, eliminating its rule over a self-proclaimed "caliphate", but the jihadists remain a threat from sleeper cells around the world.
Originally an offshoot of al Qaeda, IS took large swathes of Iraq and Syria from 2014, imposing a reign of terror with public beheadings and attacks by supporters abroad - but it was eventually beaten back to the village of Baghouz.
"We announce today the destruction of the so-called Islamic State organisation and the end of its ground control in its last pocket in Baghouz," Syrian Democratic Forces (SDF) general commander Mazloum Abdi told a victory ceremony.
SDF fighters, who besieged Baghouz for weeks while planes pounded from above, paraded in memory of 11,000 comrades killed in years of fighting against IS.
Despite the euphoria, some shooting and mortar fire continued on Saturday morning, according to a Reuters journalist at Baghouz. And Abdi warned the campaign against the militant's more hidden threats must continue.
Some IS fighters still hold out in Syria's remote central desert, and in Iraqi cities they have slipped into the shadows, staging shootings or kidnappings.
The United States believes the group's leader, Abu Bakr al-Baghdadi, is in Iraq. He stood at the pulpit of the medieval mosque in Mosul in 2014 to declare himself caliph, sovereign over all Muslims.
Further afield, jihadists in Afghanistan, Nigeria and elsewhere show no sign of recanting allegiance, and intelligence services say IS devotees in the West might plot new attacks.
Islamic State originated as an al Qaeda faction in Iraq, but took advantage of Syria's civil war to seize land there and split from the global jihadist organisation.
In 2014, it grabbed Iraq's Mosul, erased the border with Syria and called on supporters worldwide to join a jihadist utopia, complete with currency, flag and passports.
Oil production, extortion and stolen antiquities financed its agenda, which included slaughtering some minorities, slave auctions of captured women, grotesque punishments for minor crimes, and the choreographed killing of hostages.
Over the past two months, some 60,000 people poured out, fleeing SDF bombardment and a shortage of food so severe that some were reduced to cooking grass.
At the end, they were holed up in a tiny enclave from which they released a video showing fighters still shooting with smoke billowing above - an attempt to portray their last stand as heroic and a call to arms for future jihadists.
