President Robert Mugabe on Tuesday urged the military to protect Zimbabwe's natural resources, as investigators look into worries that soldiers are involved in "blood diamond" trade.

"My message to you today is for you to remain loyal to your country and jealously guard its independence, sovereignty and natural resources," Mugabe said in an address to troops to mark Defence Forces Day.

"Remain wary of renewed subtle imperialistic efforts to dispossess us of the control of our natural resources."

The military has come under international criticism after investigators documented soldiers forcing villagers to mine diamonds in the eastern Marange diamond fields.

A monitor from the global diamond trade watchdog Kimberley Process was expected to visit the Marange fields on Tuesday to confirm whether abuses have ceased ahead of an authorised sale of diamond stocks in Harare on Wednesday.

The Kimberley monitor Abbey Chikane has previously certified Zimbabwe as meeting minimum human rights standards, but his report failed to convince all the members of the scheme, which has allowed the country to make two sales of existing diamond stocks.