The regime of Syrian President Bashar al-Assad has been accused of resorting to chemical weapons after seven people died from poisonous gas fumes in an assault on Homs.
Assad's forces sprayed the al-Bayyada rebel-held neighbourhood in the western Syrian city with a poisonous gas similar to the lethal sarin, local activists told Al-Jazeera.
"The situation is very difficult. We do not have enough facemasks. We don't know what this gas is but medics are saying it's something similar to sarin gas," Raji Rahmet Rabbou, an activist in Homs, told the Qatar-based television channel.
According to Al-Jazeera dozens of people were injured in the gas attack and reported nausea, loss of muscle use, blurred vision and breathing difficulties.
Such symptoms are similar to those caused by sarin, a gas the UN has classified as a weapon of mass destruction.
A video showing Homs medics trying to revive a person suffering severe breathing difficulties has been posted on YouTube by Syrian activists, although its authenticity cannot be confirmed.
The attack came shortly after a deadly airstrike on a bakery in Hama province killed dozens.
The West has already raised concerns about the possible use of chemical weapons by Assad loyalists and warned the Syrian president about dire consequences.
In December, Foreign Secretary William Hague said that he had intelligence that the regime was preparing to use chemical and biological weapons in a desperate attempt to win the civil war.
"We and the US have seen some evidence of that and that is why we have issued strong warnings about it. We have done so directly to the Syrian regime," Hague told the BBC.
In August, US President Barack Obama warned Assad that by using chemical weapons he would cross a "red line."
"We have been very clear to the Assad regime, but also to other players on the ground, that a red line for us is we start seeing a whole bunch of chemical weapons moving around or being utilised. That would change my calculus," Obama said.