The UK Government must do more to highlight the humanitarian crisis being caused by the war in Syria, former foreign secretary David Miliband has said.
Civilians are being "bombed to hell" by Bashar Assad's forces but the UN Security Council - of which the UK is a member - has been sidelined, he said.
Former Cabinet minister Mr Miliband, who leads aid organisation the International Rescue Committee, said instability in Syria could not be confined within its borders.
"It cannot be right that civilians are being bombed to hell without the UN Security Council playing any role at all - as far as anyone can see, it has been driven off the scene," he told BBC Radio 4's Today programme.
In a message to Prime Minister Theresa May and Foreign Secretary Boris Johnson, he said: "The UK should have a foreign policy that matches the responsibility that goes with being a permanent member of the Security Council.
"At the moment the UN has been sidelined when it comes to the greatest war in the Middle East at the moment, the Syrian war.
"That cannot be in the interests of the region or, frankly, in the interests of the wider world because one of the lessons of the last seven years in Syria is that nothing that is born in Syria stays in Syria and the instability is exported beyond its borders, not confined within them."