JOHANNESBURG -- As Americans flock to stores for holiday shopping, some will buy diamonds for loved ones. But that gift could have a bloody past. If the diamonds are from Zimbabwe, the stones could have been mined under the control of Zimbabwe's army, which Human Rights Watch found has killed more than 200 people, engaged in torture and used forced labor, including children, in the nation's Marange diamond fields.

The good news is that U.S. consumers can help expose and shut down the illegal trade in these diamonds. All they need do is ask their retailers about the source of the diamonds and request the seller to ensure that the gems are not from Zimbabwe. If the retailer can't, then make it "no sale."

During several visits this year to the Marange fields for Human Rights Watch, I spoke with more than 100 people who had witnessed killings and beatings or suffered torture, forced labor, rape and the looting of their property by military officials who control informal mining syndicates. The army pilfers and smuggles out the area's rough gems, keeping the substantial profits for itself and the political party of Zimbabwe's authoritarian president, Robert Mugabe.

If mined legally, these diamonds could materially benefit a population that has been brutalized by oppressive rule and a man-made humanitarian disaster. Instead, people near the diamond fields live in abject poverty and constant fear.

A woman who had been forced to dig for diamonds told me: "The soldiers were armed and guarded us every day while we worked in the fields. Each day we worked for 11 hours without a break. The children worked the same hours." Those who resisted faced torture, beatings or even death.

"At the diamond fields, the soldiers forced us into a cage and beat us throughout the night," a boy from Mutare told me. "We were forced to fill the holes and gullies made by local miners using bare hands. We were given no food or water."

It was not supposed to be this way. Seven years ago, in the aftermath of horrific abuses committed by West African rebel groups enriched by diamond wealth, an international body backed by the United Nations - the Kimberley Process Certification Scheme - was founded to ensure that traders and consumers could identify these so-called blood diamonds and prevent their trade. The group now represents 75 countries, including Zimbabwe and the United States, and claims to cover 99 percent of the global rough-diamond industry.

But the Kimberley Process has proved to be ineffective in stamping out the smuggling and sale of blood diamonds from Zimbabwe and other countries. These gems continue to find their way into jewelry stores worldwide.

In Zimbabwe's case, blood diamonds often get smuggled onto world markets via unregistered traders in neighboring countries such as Mozambique or South Africa. These countries either don't or can't certify the origin and flow of the stones, which then become intermingled with legitimate gems.

Earlier this year, a Kimberley Process review mission found that diamonds in eastern Zimbabwe are mined under conditions of serious human rights abuses and in breach of the organization's standards, which require members to ensure that diamonds are lawfully mined, documented and exported. But the Kimberley Process works by consensus. Its members include Namibia, Russia and South Africa, which support Mugabe and which also export diamonds to the United States.

As a result of their objections, the Kimberley Process decided in November not to suspend Zimbabwe or ban the sale of its stones. Its weak excuse was a technicality in its mandate that defines blood diamonds as those mined by abusive rebel groups, not abusive governments.

It shouldn't matter who does the abusing. The Kimberley Process, by failing to do its job, leaves Americans and others in the uncomfortable position of potentially buying blood diamonds. Consumers can no longer be sure that diamonds with a Kimberley Process certificate are clean.

Our latest information is that the situation in Marange remains largely unchanged. Despite assertions that the army was withdrawing, most of the diamond fields remain under military control, with smuggling, human rights abuses and corruption unchecked.

American consumers can send a strong message to the diamond industry, the smugglers and those running these abusive mining operations: It is not acceptable to trade in stones mined by children whose labor was coerced, by women who've been raped or by men who've been tortured.

So, press your jeweler about the origin of the gems you want to buy. If they're from Zimbabwe, don't buy them. Diamond mining in Zimbabwe has inflicted great harm. U.S. consumers need to ask themselves whether that's a moral price they're willing to pay for a stone.