Britain on Friday urged the United Nations Security Council to impose sanctions on Syria after a UN-led investigation found that government forces were responsible for the sarin gas attack on Khan Sheikhun.

A joint UN-Organisation for the Prohibition of Chemical Weapons (OPCW) panel said the Syrian air force had dropped a bomb on the opposition-held town on April 4, releasing the deadly nerve agent that killed more than 80 people.

"A robust international response is now essential to hold those responsible for the Khan Sheikhun attack to account," British Ambassador Matthew Rycroft told reporters.

"It now falls on the Security Council to act on these findings and to deliver justice."

Britain is in talks with the United States on a draft resolution that would impose sanctions on Syria, the ambassador said.

Such a measure, however, would likely face a veto from Russia, an ally of President Bashar al-Assad.

Russia questioned the findings, citing many "inconsistencies" in the report and criticizing the expert investigators over the use of "doubtful witness accounts and unverified evidence."

Moscow has maintained that the sarin attack was most likely caused by a bomb set off directly on the ground, not by a Syrian air strike.

Britain has accused Moscow of "covering up" for Syria and Rycroft said Russia must "find their moral compass" and support accountability for the Khan Sheikhun attack.

US Ambassador Nikki Haley said after the report was sent to the council on Thursday that the top UN body must send a "clear message" that the use of chemical weapons will not be tolerated.

source: AFP