The Syrian Network for Human Rights in London said three people died in the alleged chemical attack. The group, whose figures were not independently confirmed, said a total of 83 people were killed in fighting across the war-torn country Wednesday.
Al-Arabiya reported the Free Syrian Army rebel group charged the chemical weapons were fired on the Damascus-area town by Hezbollah fighters and forces loyal to President Bashar Assad.
Opposition activists told the Saudi TV news channel the chemical weapons caused victims to choke.
The Syrian government claims it is the rebels who have employed chemical weapons and Friday accused the United States of manufacturing stories about chemical weapons use by the Syrian military to justify support for the rebels. Russian President Vladimir Putin has said he finds the U.S. charges unconvincing.
U.S. State Department spokeswoman Jen Psaki Friday told reporters the United States would be sending support to the rebels but didn't reveal specifics.
Britain's government has expressed support of the U.S. findings.