(CNN) -- Rebel forces and Syrian President Bashar al-Assad's government are blaming each other for the latest reported use of poisonous gas in the ongoing civil war.
The opposition contended Saturday that attacks wounded dozens in Hama and Idlib provinces.
Video clips posted on anti-government websites showed a number of civilians, including children, appearing to have difficulty breathing and using oxygen masks.
CNN could not independently confirm the authenticity of the videos because the Syrian government limits access to international journalists.
There were no reports of deaths Saturday related to the incidents in the towns of Kafr Zeita and Al-Tamanaa, both rebel strongholds.
On Friday, six people died in chlorine attacks on Kafr Zeita and dozens injured were injured, according to the opposition Local Coordination Committees of Syria. Another opposition group, the Syrian Observatory for Human Rights reported government helicopters dropped barrel bombs on Kafr Zeita in the northern countryside of Hama at the same time rebels reported the use of poisonous gas.
According to the Hama Media Center, an opposition activist group, at least 50 civilians showed sign of illness after chlorine gas was used again on Kafr Zeita on Saturday. Opposition sources said oil drums filled with explosives also were dropped.
Videos posted online purport to show a number of Kafr Zeita civilians, including children, suffering from suffocation and showing poisoning symptoms, according to a medical professional in a makeshift health clinic.
Another video posted Sunday by an anti-regime group purports to show the aftermath of a government attack on the village of Al-Tamanaa in south Idlib countryside. It shows people receiving treatment for breathing difficulties.
Activists said they could not determine the nature of the chemical agent believed to have been used.
State television had reported Saturday that the al Qaeda-linked al-Nusra Front was preparing to strike two communities -- Wadi al-Deif in Idlib and Morek in Hama -- with chlorine or sarin gas.
Wadi al-Deif is home to a government army base, one of its last significant posts in the northern province of Idlib. The base is surrounded by opposition-controlled areas.
Morek, a rebel stronghold, has been witnessing violent clashes between the al-Assad troops and the opposition fighters. It is a few miles from Kafrzeita.