The warning came after the US, UK and France struck three Syrian sites in response to a suspected deadly chemical attack in the town of Douma a week ago.
Syria denies any chemical use and says that attack was fabricated by rebels.
A UN Security Council vote brought by Syria's ally, Russia, and condemning the US-led strikes was rejected.
The wave of strikes represents the most significant attack against President Bashar al-Assad's government by Western powers in seven years of Syria's civil war.