Britain and France called today for UN sanctions to be imposed on after a UN-led investigation found the regime had carried out chemical attacks.

The UN ambassadors from London and Paris described the use of chemical weapons against civilians as a war crime ahead of a council meeting to discuss the investigation's findings.

"France favours a quick and strong Security Council response," said French Ambassador Francois Delattre.

This would provide for "imposing sanctions on those who are responsible for these acts, which are constitutive of war crimes and crimes against humanity," he told reporters.

US Ambassador Samantha Power did not specify what measures should be taken, but called on the Security Council to act swiftly to ensure those responsible for using chemical weapons "pay a price."

An investigative panel set up by the Security Council said in a report last week that President Bashar al-Assad's forces had carried out at least two chemical attacks, one in 2014 and one in 2015.

Previous reports from the Organisation for the Prohibition of Chemical Weapons (OPCW) had concluded that toxic gases have been used as weapons in Syria's five-year war, but stopped short of identifying the perpetrators.

The panel of inquiry, known as the Joint Investigative Mechanism (JIM), for the first time pointed the finger of blame at the Assad regime for chemical weapons use after years of denial from Damascus.

British Ambassador Matthew Rycroft said the council will be "looking at the imposition of sanctions and some form of accountability within legal mechanisms."

Rycroft said it was "essential that we have a robust response" to impose "measures under chapter 7" of the UN charter, which provides for sanctions.

The push for sanctions against is expected to face resistance from Russia, Syria's ally.

Russian Ambassador Vitaly Churkin praised the JIM for its professionalism, but declined to say what measures might be taken to follow up on the panel's findings.

The panel found that the Syrian regime had dropped chemical weapons on two villages in northwestern Idlib province: Talmenes on April 21, 2014 and Sarmin on March 16, 2015.

In both instances, Syrian air force helicopters dropped "a device" on houses that was followed by the "release of a toxic substance," which in the case of Sarmin matched "the characteristics of chlorine."

Chlorine use as a weapon is banned under the Chemical Weapons Convention, which joined in 2013, under pressure from Russia.