Boris Johnson has lashed out at Russia for "covering up" for the Syrian government over its use of chemical weapons following the release of a damning UN report.
The Foreign Secretary accused Moscow of undermining international efforts to prevent the use of the banned weapons after consistently backing up "abhorrent ally" Bashar Assad, who has been accused of killing scores of his own people with poison gas.
Mr Johnson was commenting on a report by the UN and the chemical weapons watchdog that said they were "confident" that the Syrian government was behind a sarin gas attack that claimed more than 90 lives.
He accused Russia of repeatedly attempting to "disrupt efforts to get to the truth" since the attack on Khan Sheikhoun in April, first by denying sarin was used then vetoing a UN Resolution on Tuesday that would have extended the investigators' mandate.
"Russia has consistently chosen to cover up for Assad. This was the ninth veto it has used to protect Assad and the third it has cast to prevent the Assad regime from being held accountable for its poison gas attacks," Mr Johnson said.
"This behaviour can only undermine the global consensus against the use of chemical weapons. I call on Russia to stop covering up for its abhorrent ally and keep its own commitment to ensure that chemical weapons are never used again."
The attack on Khan Sheikhoun drew widespread international condemnation of the Syrian government, although Damascus and Moscow have denied the atrocity.
On Thursday, the Organisation for the Prohibition of Chemical Weapons and United Nations' Joint Investigative Mechanism said its experts were "confident that the Syrian Arab Republic is responsible for the release of sarin on April 4 2017".
Images from the massacre shocked the world and Mr Johnson said it was clear that the Assad regime's actions had "tragic consequences for hundreds of victims".
The Foreign Secretary decried that, despite Russia backing a 2013 agreement to destroy Syria's chemical weapons stockpile, investigators had since uncovered evidence of four separate attacks using the munitions.
"Britain condemns this appalling breach of the rules of war and calls on the international community to unite to hold Assad's regime accountable," he said.