KABUL, Afghanistan — More U.S. military deaths in the last 10 months of the Afghan war than in the first five years of the conflict. More boots on the ground than in Iraq.

As the U.S. military death toll in the Afghan conflict reached the 1,000 mark, a fight that has become "Obama's war" now faces its greatest challenge -- a high-risk campaign to win over a hostile population in the Taliban's southern heartland.

More casualties are expected when the campaign kicks into high gear this summer. The results may determine the outcome of a nearly nine-year conflict that has become the focus of America's fight against Islamist militancy.

The 1,000 U.S. military death occurred in a roadside bombing Friday -- just before the Memorial Day weekend when America honours the dead in all its wars.

A NATO statement did not identify or give the nationality of the victim. U.S. spokesman Col. Wayne Shanks said the trooper was American -- the 32nd U.S. war death this month by an Associated Press count.

The list of U.S. service members killed in combat in Afghanistan begins with Sgt. 1st Class Nathan Ross Chapman of San Antonio, Texas, a 31-year-old career Special Forces soldier ambushed on Jan. 4, 2002, after attending a meeting with Afghan leaders in Khost province.

He left a wife and two children. The base where a suicide bomber killed seven CIA employees last December bears his name.

The AP bases its tally on Defence Department reports of deaths suffered as a direct result of the Afghan conflict, including personnel assigned to units in Afghanistan, Pakistan or Uzbekistan. Other news organizations count deaths suffered by service members assigned elsewhere as part of Operation Enduring Freedom, which includes operations in the Philippines, the Horn of Africa and at the U.S. detention facility at Guantanamo Bay, Cuba.

The grim milestone reflects the acceleration in fighting since President Barack Obama shifted the focus from Iraq to Afghanistan, where al-Qaida plotted the Sept. 11, 2001 terror attacks in the United States.

Yet Obama's decision brought a heavy price.

In the last 10 months, at least 313 U.S. service members have been killed in the war -- more than the 295 who died in the first five years of the conflict. More than 430 of the U.S. dead were killed since Obama took office in January 2009.

The number of U.S. troops in Afghanistan has now surpassed the total in Iraq -- roughly 94,000 in Afghanistan compared with 92,000 in Iraq. In 2008, the U.S. force in Afghanistan numbered about 30,000.

For many of the U.S. service members in Afghanistan, the 1,000-mark passed without fanfare.

Capt. Nick Ziemba of Wilbraham, Massachusetts, serving with the 1st Battalion, 17th Infantry Regiment in southern Afghanistan, said 1,000 was an arbitrary number and would have no impact on troop morale or operations.

"We're going to continue to work," he said.

At least 675 troops from allied countries have also died in the war, according to an AP tally based on announcements of foreign governments. They include 288 service members from Britain.

Establishing the number of Afghan dead is far more difficult, particularly for the first years of the war. The United Nations reported in January that an increasing number of Afghan civilians have been killed over the past three years, with a total of at least 6,053 since 2007.

The 1,000th U.S. death comes midway between Obama's decision last December to send 30,000 more U.S. troops to Afghanistan and a review of the war's progress that he has promised by the end of the year.

After a long and wrenching conflict in Iraq -- which has claimed nearly 4,400 American military lives -- Obama has promised not to be backed into an open-ended war in Afghanistan. He has insisted that some U.S. troops will come home beginning in July 2011.

That has not been enough to satisfy his anti-war supporters. At the same time, mid-2011 may be too soon to turn the tide of the war.

As casualties rise, the slide in overall support for the war may accelerate.

A majority of Americans -- 52 per cent -- say the war is not worth the cost. The negative assessment in a new Washington Post-ABC News poll followed a brief rise in support for the war after Obama refocused the U.S. war plan last year.

Those figures could change dramatically depending on the outcome of the coming operation in Kandahar, the biggest city in the south, with about a half million people, and the Taliban's former spiritual headquarters. U.S. commanders believe Kandahar is the key to the ethnic Pashtun south, the main theatre in the war.

The operation will pose the greatest test for the U.S. counterinsurgency strategy, which focuses on protecting civilians, bolstering the Afghan government and rushing in economic development to win public support. It is also expected to lead to a spike in U.S. casualties, even though the military says the campaign will include very little traditional combat.

Winning over the southern population won't be easy. Many Pashtuns, who form the overwhelming majority of the Taliban, view the central government as corrupt and ineffectual, dominated by rival communities of ethnic Tajiks, Hazaras and Uzbeks.

Many Pashtuns prefer negotiations with the Taliban, even if talks end with a significant political role for the Islamist movement.

"The Taliban are not outsiders. They are our own people," said Kandahar farmer Raaz Mohammad. "They should sit and resolve the situation. This is the only thing they can do if they want peace over here."

Among many rural southern Pashtuns, years of deteriorating security, rising crime and corrupt administration have blurred memories of the economic hardship, harsh rule and subjugation of women that were hallmarks of the Taliban when they ran most of the country from 1996 until the U.S.-led invasion of 2001.

"I am living here since birth and I think the Taliban time was much better than this," said Neda Mohammad, a Kandahar businessman. "The only thing that we were missing at that time was a hospital. Otherwise, we were much better then than now. Why do the Americans think they can win? They can't win and they know that."

The challenges of winning over a reluctant and intimidated population have become clear in the wake of last February's operation to clear Marjah, a southern farming community of about 80,000 people in Helmand province west of Kandahar. U.S. Marines and Afghan forces seized the community in about two weeks of fighting, rushing in an Afghan administration to begin development projects and restore public services.

Three months later, officials acknowledge that progress in winning public support has been slow. Taliban fighters simply hid their weapons and blended in with the population. Through a clandestine campaign of assassination and intimidation, the Taliban have slowed development projects because people are afraid to co-operate with the coalition.

"The Taliban are moving back into Marjah and getting stronger," said Col. Kamaluddin, a deputy provincial police chief who uses only one name.

For coalition soldiers on the ground, the main task is to perform the mission with as few casualties as possible.

"We understand what we were getting into and we understand that it's something that has to be done," Staff Sgt. James Knower of Pavilion, N.Y., said at a base in Kandahar. "I would never think that what we've done here is a waste of time. We're going to the end."

Of American casualties, he added: "It's war. It's going to happen."