WASHINGTON — U.S. and NATO air bombings in Afghanistan have killed more than 500 civilians since 2006, fueling a public backlash against the coalition's war effort, a prominent human rights group said today.

Human Rights Watch, an international organization based in New York, blamed some of the civilian deaths on Taliban and al-Qaida insurgents who create "human shields" by blending into populated areas.

But the group also criticized mainly U.S. commanders for launching bombing raids under looser military "rules of engagement" than those followed by other NATO nations with troops in Afghanistan.

"The United States needs to end the mistakes that are killing so many civilians," said Brad Adams, Asia director for Human Rights Watch.

"While Taliban shielding is a factor in some civilian deaths, the United States shouldn't use this as an excuse when it could have taken better precautions."

Though suicide bombings and other insurgent attacks have killed about twice as many civilians as U.S. and NATO missions, the airstrikes launched mainly by Americans have caused deep resentment, the group said.

Blair Jones, a White House spokesman, said U.S. military commanders exercise caution in Afghanistan.

"The United States takes steps to avoid civilian casualties in all its operations," Jones said. "As the report notes, the Taliban often use civilians as human shields to cover their activities against the Afghan people and Afghan government."

Jones added, "We grieve for every loss of life and will continue to take measures to avoid the deaths of innocent civilians."

A U.S. airstrike July 6 killed 47 Afghans at a wedding in Nangahar province, and nine Afghan national police officers died in a U.S. bombing raid in Farah province two weeks later.

In response to an airstrike two weeks ago, the Afghan government began a review of foreign troops' presence in the South Asia country.

"In winning the tactical battle quickly on the ground with bombs, U.S. and NATO forces risk losing the strategic battle for the support of the population, essential in counterinsurgency operations," the report said.

The U.S. willingness to employ airstrikes when its troops aren't under direct attack prompt concerns that Washington is snubbing its obligations under the Geneva Conventions and other international laws of war, Human Rights Watch said.

Lt. Col. Mark Wright, a Pentagon spokesman, said Taliban and other insurgent forces often attack U.S. troops from inside civilian homes.

"Every death of a civilian in wartime is a terrible tragedy," Wright said. "That being said, U.S. forces are in Afghanistan to support the Afghan people and their government."

The number of overall Afghan civilian deaths in the war, which the United States launched in October 2001 after the Sept. 11 terrorist attacks, rose from 929 in 2006 to 1,633 last year, according to the Human Rights Watch report.

About 540 civilians died in the first seven months of this year, the report said, which projects to a 2008 total of 926 — almost exactly the 2006 figure.

Coalition airstrikes killed 556 civilians between the start of 2006 and the end of this July, while 530 died in U.S. and NATO ground attacks.

Some NATO officials told the human rights group's analysts that the United States, which controls most of the sky over Afghanistan, relies too much on air power.

"Some Afghans think the United States is worse than the Russians," one ambassador in Kabul, the nation's capital, told the group.

The Soviet Union occupied Afghanistan from 1979 to 1989 and controlled a Communist puppet government there for three years after its military forces withdrew.

There are 42,550 U.S. troops in Afghanistan, with 23,550 operating under NATO control and 19,000 in direct U.S. control as part of Operation Enduring Freedom.