The European Union announced Monday that Zimbabwe could go ahead with some diamond and gold sales in Europe provided it has democratic elections as expected in July.
The European Union said it was "encouraged" by political reforms ahead of "peaceful, transparent and credible elections later this year."
Global Witness said, however, there may be gaps that give the government a chance to funnel revenue from diamond sales to the military.
Campaigner Emily Armistead, in a statement, said the advocacy group welcomed the fact that some restrictions against ZMDC remained in place.
"However, the EU could have gone further to prevent diamond revenues funding ZANU-PF security forces," she said. "In particular, we are concerned that Zimbabwe's largest diamond company, Anjin, is part-owned by the military but is not covered by restrictive measures."
The group said there were links between diamond mining companies and security forces loyal to Zimbabwean President Robert Mugabe. Global Witness said some of those groups were tied to political violence that erupted when elections last took place in Zimbabwe in 2008.