Until now, the world's leading chemical weapons expert could only say if chemicals were used — but not specify who used them.
That changed on Wednesday after the Organisation for the Prohibition of Chemical Weapons (OPCW) granted itself new powers to assign blame.
It comes despite protests by Russia, who said the move went "beyond the mandate" of the watchdog.
Members of the OPCW voted 82-24 for the measure at a conference in The Hague, which surpassed the two-thirds majority needed.
The motion was proposed by the UK, and Britain's Foreign Secretary Boris Johnson welcomed the move. He said: "Chemical weapons are an affront to human dignity and have no place in the 21st century."
He added: "The international community has quite rightly come together today to strengthen the ban on chemical weapons and prevent impunity for their use."
Tensions between the UK and Russia have escalated following the attempted murder of former Russian double agent Sergei Skripal and his daughter.
Syria's government has repeatedly faced allegations of chemical weapons use against rebels and civilians.
The US, Britain, and France jointly bombed three government sites in Syria, in response to an alleged chemical attack in April.
The Syrian government, which is backed by Russia, denies ever using chemical weapons.