David Miliband has warned that the crisis in Zimbabwe risks "infecting" the whole of southern Africa.
The foreign secretary spoke of the wider dangers as he met refugees from Robert Mugabe's regime in neighbouring South Africa.
He called for tougher sanctions, and insisted it was "imperative" that a new Government was formed which represented the will of the Zimbabwean people.
"This is now a crisis that is infecting the whole of southern Africa, and one that is a man-made tragedy from the top of the Zimbabwean regime," he told reporters.
Mr Miliband said the world should now unite around "tough, strong, clear" sanctions currently being drawn up by the UN.
The foreign secretary was visiting the Central Methodist Church in Johannesburg, which has been providing assistance to refugees crossing the border from Zimbabwe.
