The announcement came despite a call from the Kimberley Process, which works to end the sale of "blood diamonds", for the demilitarisation of the Marange fields, where security forces are accused of torture, killings and other abuses against civilians.
"The officer commanding Manicaland province, senior assistant commissioner Munorwei Shava Mathuthu, said security forces will remain in place to deal with illegal diamond dealers and panners," said the statement read on state television.
Mines Minister Obert Mpofu "concurred with the security forces", state television added — although on Sunday the government had said it would conduct a phased withdrawal from Marange.
A team from the Kimberley Process on Wednesday accused the military of being involved in illegal diamond mining in the Marange and of perpetrating "horrific" violence against civilians.
The team recomended that Zimbabwe remove the army from Marange by July 20.
The team visited Zimbabwe last week on a fact-finding mission, after Human Rights Watch accused the armed forces of using torture and forced labour to control the Marange fields, saying 200 people had been killed last year.
Zimbabwe has denied the allegations.
The Kimberley Process was launched in 2003 to stop the flow of conflict diamonds into the mainstream market following wars in Sierra Leone and Liberia. Zimbabwe has two other diamond mines, Murowa and River Ranch, which are Kimberley certified and are not involved the claims of abuses.