Boris Johnson has offered Russia a chance to end the Syria crisis saying “they still have time to be on the right side of the argument” as he warns that the United States may strike again.
The Foreign secretary also branded Syrian President Bashar al-Assad an “arch-terrorist” and pledged that the UK and allied forces would gather evidence for “war crimes prosecutions for those responsible”.
Mr Johnson went on the front foot after he was criticised for failing publicly to persuade G7 countries to agree to a sanctions against Russia for its support of the Assad regime.
Relations with Moscow were strained when President Donald Trump ordered a missile strike against the Syrian airfield from which a chemical weapons attack was launched on civilians.
The gas attack had killed 70 people, many of them children who were filmed dead or dying, frothing at the mouth.
Mr Johnson then cancelled a visit to Moscow and threatening sanctions against Russia and Syria, a promise which backfired when the Germans and Italians refused to agree until an investigation has been carried out into who was to blame for the nerve gas attack in Idlib province.
In an article for The Sunday Telegraph, his first wide-ranging remarks since the row, Mr Johnson appealed to Moscow to help stop the killing.
He said: “Assad uses chemical weapons because they are not only horrible and indiscriminate.
“They are also terrifying. In that sense he is himself an arch-terrorist, who has caused such an unquenchable thirst for revenge that he can never hope to govern his population again.
“He is literally and metaphorically toxic, and it is time Russia awoke to that fact. They still have time to be on the right side of the argument.”
Mr Johnson said there was no doubt that a bomb dropped from two Syrian U-22 planes which “took off from an airbase where chemical weapons have been stored” were behind the attack.
He said: “British scientists have analysed samples from the victims of the attack. These have tested positive for sarin or a Sarin-like substance.