The Zimbabwean government has announced it will summon mining companies in the controversial Chiadzwa diamond fields to ask why their revenues are so low.

A top government official says diamond production targets are not being met in the rich gem fields, currently mined by companies linked to the Chinese and President Robert Mugabe's ruling party.

Until now President Robert Mugabe’s party has blamed official low revenues on Zimbabwe’s diamonds on sanctions but now the mining ministry is taking a different tact.

Deputy Minister Fred Moyo says mining companies working in the Marange fields have been summoned to explain why they are not making the profits they promised.

Moyo told the Sunday Mail the boards of the state mining corporation and the minerals marketing corporation are also to be revamped.

He admits Zimbabwe is not efficiently producing its diamonds.

As predictions grow that Zimbabwe’s economy is slipping into a second down turn, the authorities need to boost revenue more than ever from the sector that has been blighted by allegations of smuggling and lack of transparency.