In the woodlands of southern Zambia hunger arrives with the rhythmic clack of stone against stone as villagers pound open the hard mungongo nuts, a food of last resort for which they compete with monkeys and elephants. The pounding is the only sound in hamlets such as Siatumbu where families slump in front of thatched huts, weakened and tired.

The matriarch, Muntimba, has witnessed drought many times and this one is the worst, she says. "The children cry themselves to sleep from hunger. We go further into the bush to find nuts and berries, but it's not enough. If this goes on we'll die."

In a neighbouring village, the headman, David Bouvu, 71, sits in the shade of a tree, shaken by rebellion. "The children refused to go to school today. They said they were too weak to walk or concentrate. That never happened before, no matter how bad it got."

There are no confirmed deaths from starvation, but the villagers are becoming anaemic and those with Aids are deteriorating as immunity systems collapse.

In the nearest town, Livingstone, several thousand tonnes of emergency relief maize sits in a warehouse with frosted windows on Industrial Road, untouched since arriving in July. Mr Bouvu knows of the food aid.

"The GM? Yes, the radio says it's poison."

Would he eat it? "If it was in front of me now, yes."

A food crisis threatens more than 14 million people in six countries in southern Africa, the result of drought, floods and bad policies. As the crisis deepens so does an anguished debate: should the countries accept genetically modified maize, donated mostly by the US. The maize has been rejected by Zambia and has aroused suspicion in other states concerned about the impact on health, the environment and trade.

International environment and development groups accuse the US of manipulating the crisis to benefit the biotech corporations, and of using the UN to distribute domestic food surpluses which cannot find a market. America responds that hysteria stoked by Europeans is endangering starving people.

Swaziland and Lesotho have accepted the GM maize. Mozambique, Malawi and Zimbabwe insist it is milled into flour, so that farmers cannot plant the seed. Zambia, with almost 3 million hungry, has rejected it in any form.

The government claims there are enough alternative food sources to feed its people until the harvest in March, and that the risk of famine is overstated. "We are confident we can cope without GM," said the agriculture minister, Mundia Sikatana, citing stockpiles of home-grown maize and cassava and commercial food imports.

Maize dealers and millers are suspected of hoarding in expectation of price rises. Posing as a buyer wanting 500 tonnes, the Guardian was assured by two local transport companies that the order could be sourced and delivered to anywhere in Zambia within days.

A manager at Olympic Milling, based in the north, said he was sitting on 45,000 tonnes, and that fresh imports were arriving, lured by the high prices. "But farmers and millers are not releasing anything. There are many people committed to high prices."

It is unclear if these sources would be enough. Aid agencies despair over the lack of reliable data. Britain's Department for International Development estimates that without the GM maize, only half of the required food will reach the hungry. GM would close most, but not all, of the gap.

Richard Ragan, the head of the World Food Programme in Zambia, says the aid pipeline is broken. "Because of the restrictions on what we can distribute, we are only reaching half of the people in need."

A field worker for the aid agency Care, Robbie Mwiinga, says that disease and malnutrition are rising because people are receiving less than 350g of other food aid a day.

Rising tensions



Aid agencies accept that the government has the right to reject food it deems unsafe, but they privately denounce it for waiting until August, five months into the crisis, to ban the bulk of relief food.

Tensions have risen over the GM stockpiles, which the WFP imported before the government ban. Suspecting it was in danger of rotting, villagers in Kalomo demonstrated for handouts, and crowds in Monze and Nangoma looted a ware house. Aid workers in Southern Province, the worst-hit area, say the ban is hurting the enfeebled and destitute, but that mass deaths are not inevitable if more food comes soon. "It's a gamble," said one.

The government insists that the risks of GM food are too great. Groups such as ActionAid and Greenpeace warn that GM crops would threaten biodiversity and make subsistence farmers dependent on the biotech companies. Nor would the EU accept Zambian food imports deemed "contaminated".

Milling the seed would eliminate those concerns, most non-governmental organisations agree. Several donors, including Britain, have offered to pay for the milling, but the government says the seeds could be stolen and planted. President Levy Mwanawasa is even more worried about the impact of eating GM, milled or not. Branding it "poison", he has said he will not sacrifice Zambian lives by accepting modified food.

Americans and Europeans may have been eating GM food for seven years without detectable harm, but there is no long-term proof it is safe, said Mwananyanda Lewanika, a Mississippi-trained biochemist and the president's scientific adviser. Maize is the staple diet of Zambian villagers and they would be vulnerable should it turn out to give them allergies or resistance to antibiotics.

Arrest threat



Dr Lewanika was part of a Zambian delegation which recently toured the US and Europe on a GM fact-finding mission. The group has submitted a report to the president and an announcement is expected soon on whether to lift the ban. "Personally, I don't think we should permit GM in any form until we have our own regulatory mechanism set up," he said.

The debate is no longer about science, but about politics. The president, elected last year in a controversial ballot, has stifled dissent. State radio and newspapers echo his concern about GM and play down the food crisis. An MP who alleged in parliament that three constituents had starved to death was threatened with arrest.

"Now that the opposition have come out in favour of GM, the president can't back down without looking weak," said one diplomat. "And his policy is popular with the urban elite; they like the idea of standing up to the US."

Interviews with Zambia's agriculture and health ministers also suggest that relations with the WFP have broken down because of personality clashes and suspicion that the UN food agency is beholden to US commercial interests.

Certain groups advising the government have vested interests. The National Institute for Scientific and Industrial Research, long-starved of resources, would run the "regulatory mechanism". Millers and farmers sitting on stockpiles know prices will fall if GM or any other type of relief food floods the market.

Analysts say, however, that the imbroglio would not exist were it not for the US system of tied aid. Instead of donating mostly money, as the EU does, to let those handling a crisis buy food on the open market, Washington donates subsidised GM food grown only in America. It is allegedly a covert, additional subsidy to its farmers.

If the aid agencies had cash rather than maize they could resolve the crisis without touching GM, said Guy Scott, a former Zambian agriculture minister. "But it is the official policy of USAid (the US agency for international development) to promote GM."