Boris Johnson has said he is “dismayed” at Russia’s veto of a UN resolution condemning the use of chemical weapons in Syria.
The foreign secretary urged the country to stop acting “as a lifeline for Assad’s murderous regime”.
World leaders had wanted an investigation into the chemical attack in Idlib last week, which prompted a retaliatory US missile strike.
But Russia, an ally of Syria, used its powers in the UN to block it.
The attack on the town of Khan Sheikhoun last Tuesday left 89 people dead and hundreds injured.
The US and its allies blamed the Syrian government, and two days later the US fired 59 cruise missiles at Syria’s Shayrat airbase in response.
Syrian President Bashar al-Assad denied carrying out a chemical attack.
‘Russia faces a choice’
Russia vetoed a motion brought to the UN Security Council which would have required the Syrian government to cooperate with investigators.
It is the eighth time Moscow has used its veto to protect Syria.
Mr Johnson said: “This afternoon in New York, the international community sought to make clear that any use of chemical weapons by anyone anywhere is unacceptable and that those responsible will face consequences.
“So I am dismayed that Russia has once again blocked the UN Security Council and in so doing refused to condemn the use of chemical weapons or support a full UN investigation into the attack.”
He also backed US calls to find a political solution and said the G7 leaders were ready to work with Russia to end the violence in Syria.
“So Russia faces a choice: it can continue acting as a lifeline for Assad’s murderous regime, or it could live up to its responsibilities as a global power, and use its influence over the regime to bring six long years of failed ceasefires and false dawns to an end.”
The vote comes after a meeting between US Secretary of State Rex Tillerson and Russian minister Sergey Lavrov in Moscow to talk about the Syrian situation.
Earlier this week, G7 nations failed to agree on a proposal by Britain for sanctions against Russia following the attack.
However, Mr Johnson said there was a “large measure of support” for the plan.