They, together with the World Diamond Council, are asking international diamond traders not to touch Marange diamonds.

ECONOMIST: Zimbabwe and its diamonds

It is near an area known as Zengeni in Marange, said to be one of the world's most significant diamond fields.

BBC: Marange diamond field: Zimbabwe torture camp discovered

Finance Minister Tendai Biti, from Tsvangirai's party, has often accused the Marange mines of not remitting diamond proceeds to the Treasury.

MSN: Zimbabwe diverts $2 billion in diamonds: gem watchdog

The Marange area, 400 km (240 miles) east of Harare, has generated controversy since 20, 000 small-scale miners invaded the area in 2008 and were forcibly removed by soldiers and police.

MSN: Zimbabwe diverts $2 billion in diamonds: gem watchdog

The ban was imposed by the Kimberley Process (KP), the international organisation that polices diamonds, following reports of large-scale killings and abuse by Zimbabwe's security forces in the Marange diamond fields.

BBC: Marange diamond field: Zimbabwe torture camp discovered