The foreign secretary said he had “no doubt” President’s Bashar al-Assad’s government was behind April’s atrocity.
Russia blocked a UK-backed move at the United Nations to condemn the attack.
Mr Johnson is now appealing to world leaders to “unite behind the need to hold those responsible to account” by imposing further sanctions.
He was speaking after The Organisation for the Prohibition of Chemical Weapons (OPCW) found the deadly attack on Khan Sheikhoun, a town in Northern Syria held by rebel forces fighting the regime, on 4 April, could only be “determined as the use of sarin, as a chemical weapon”.
Source: for MORE