NATO forces, led by thousands of U.S. Marines, are massing for an attack on Marjah, billed as the last big Taliban stronghold in Helmand, Afghanistan's most violent province and heartland of its opium industry.
The operation, one of the biggest of the 8-year-old war, will be the first big show of force since President Barack Obama ordered 30,000 more troops to Afghanistan last December.
Commanders are under pressure to achieve decisive military gains this year to turn the tide in the war, before troops begin to withdraw, which Obama says will happen in mid-2011.
Hundreds of civilians have so far left Marjah, but NATO has advised villagers to stay in their homes and not flee, and most of the population, estimated at up to 100,000, has stayed put.
"We have been assured both by our forces and by international forces that they will make sure that this operation is conducted in a way that has minimum impact on civilians, and hopefully no casualties in terms of civilians in the area," Karzai's spokesman, Waheed Omer, told a news conference on Wednesday.
"Our information is that about 100 families have left the Marjah area and we have enough food items for about 6,000 families," Omer said. NATO and provincial authorities say fewer than 200 families have fled so far. An Afghan family averages around six people, though many are much larger.
British forces have already begun small-scale "shaping" operations in the area around Marjah. The International Committee of the Red Cross said "increasing numbers of war casualties" have already been arriving at a clinic it runs in Marjah.
"Civilians and injured fighters are finding it more and more difficult to go to places where they can obtain care, owing to mounting security problems and numerous roadblocks and checkpoints throughout Helmand province," it said in a statement.
Human rights groups say that since NATO has encouraged people to stay, it bears an additional legal and moral responsibility to avoid heavy fighting that would cause civilian casualties.
"It would be better if they had relocated all the civilians before any massive military battle," said Anwar Khan, a shopkeeper in the provincial capital Lashkar Gah.
"The Taliban hit and run and will hide where civilians will be at great risk," he said. "I don't know if the Taliban will ever be defeated, but many innocent civilians will lose their lives."
The assault on Marjah, a densely-populated warren of desert canals, is intended to be a demonstration of NATO commander General Stanley McChrystal's counter-insurgency strategy, which emphasizes seizing control of population centers.
McChrystal has strongly emphasized precautions to avoid killing civilians, and the number of civilians killed by NATO troops has declined since he took command in mid-2009.
During the next year, NATO troops say they plan to open roads and bring government institutions to wide swathes of Helmand and neighboring Kandahar now under the grip of insurgents.
Western leaders have signaled new backing for efforts by Karzai to reach out to insurgents for reconciliation, moves dismissed by the Taliban as a sign of weakness and desperation.
Omer said Karzai would next week formally announce a "peace jirga," or conference of elders, designed set conditions for a future peace process. Taliban members will be invited to attend, but only if they renounce the use of force first, he said.
Helmand and Kandahar are the heartlands of Afghanistan's huge opium industry, which supplies more than 90 percent of the world's crop of the raw material for heroin.
In a setback, a U.N. survey said efforts to curb opium planting had failed over the past year, with farmers planting as much opium for the upcoming 2010 harvest as last year's, ending a positive trend of two years of declines.
"The message is clear: in order to further reduce the biggest source of the world's deadliest drug, there must be better security, development and governance in Afghanistan," said Antonio Maria Costa, head of the UN Office on Drugs and Crime.