Rebel forces in Syria claimed that regime forces used chemical weapons in an attack on Homs Sunday, killing six people and injuring dozens more with poison gas.

Qatar-based satellite channel Al Jazeera reported 10 people suffered serious injuries from the chemical attack, including blindness and paralysis, and over 50 more suffered other injuries.

Opposition activists posted a video online that they claimed shows a victim of the alleged chemical attack suffering from breathing difficulties.

The international community has raised concerns that Syria’s large chemical weapons store could be used against the rebels, or fall in opposition hands. Reports have ramped up over recent weeks that embattled Syrian President Bashar Assad has been preparing to use chemicals as the country’s 21-month-old civil war rages on.

The US has called the use of chemical weapons a “red line” that may invite international intervention. On Saturday, Russian Foreign Minister Sergei Lavrov said the Syrian government had moved the chemical weapons from many arsenals to just “one or two centers” to properly safeguard them.

The attack came on a particularly deadly day for Syria. Near Hama, another rebel stronghold, more than 60 people were killed in an air strike on a bakery. Opposition sources said over 180 people were killed around the country on Sunday.