Britain last week informed the United Nations of "new incidents" of apparent chemical weapons use in Syria, diplomats said Wednesday.
If confirmed, the attacks would heap further pressure on Western countries supporting Syrian rebels to intervene in the conflict, which the United Nations says has claimed more than 70,000 lives.
President Barack Obama has called the use or movement of chemical weapons a "red line," but has thus far ruled out greater US involvement despite increasing reports of limited chemical attacks by regime forces.
London sent a letter to the world body that included "details of new incidents since April," a Western diplomat said.
Signup to our newsletter and follow us on Facebook and Twitter!
Britain and France sent three letters to the world body in April detailing the suspected use of chemical weapons in Syria, including in the embattled Homs region in December 2012.
The United Nations has appointed a team of investigators led by Swedish arms inspector Ake Sellstrom, but they have not been granted permission to enter Syria by President Bashar al-Assad's regime.
"We continue to inform the secretary general and Mr Sellstrom of any information as and when we get information of alleged chemical weapons use," Britain's UN envoy Mark Lyall Grant said, without providing further details.
A top UN envoy said last week there are "mounting reports" of the use of chemical weapons in Syria's civil war and called on the Damascus government to let in UN investigators.
The US administration said on May 15 that it believed small amounts of chemical weapons had been used at least twice in Syria but that it was awaiting full confirmation.