An operation the American military at first described as a "precision strike" instead killed 13 Afghan civilians and only three militants, the U.S. said Saturday, three days after sending a general to the site to investigate.

Civilian casualties have been a huge source of friction between the U.S. and Afghan President Hamid Karzai, who has stepped up demands that U.S. and NATO operations kill no civilians and that Afghan soldiers take part in missions to help prevent unwanted deaths.

A U.S. military statement said the decision to dispatch a general to the western province of Herat to investigate shows how seriously the U.S. takes civilian casualties. The U.S. rarely releases the findings of civilian casualty investigations, and the disclosure this time could show the effect of Karzai's criticisms.

The U.S. military originally said 15 militants were killed Tuesday in a coalition operation in the Gozara district of Herat province, but Afghan officials said six women and two children were among the dead, casting doubt on the U.S. claim.

Afghan officials say the group targeted in the airstrikes were living in two tents in a remote area. An ethnic group of Afghans known as Kuchis travel the countryside with livestock and live in tents. Photographs obtained by The Associated Press from the site showed the body of a dead young boy — bloodied and dirtied.

In response, Brig. Gen. Michael Ryan traveled to the site to meet with Afghan elders. Investigators found weapons and ammunition, but concluded that 13 civilians were killed along with three militants, the U.S. said.

An expert on civilian casualties said she was "cautiously optimistic" the U.S. is taking a new approach in dealing with civilian casualties. Sarah Holewinski, the executive director of The Campaign for Innocent Victims in Conflict, said more high-ranking military officials are visiting gravesites and apologizing.

In recent weeks, she said, Defense Secretary Robert Gates "turned the old way of doing things on its head."

"Instead of immediately denying civilian deaths, which deeply angers Afghans and with good reason, he said the U.S. will instead immediately investigate, make apologies and provide amends where appropriate," she said.

The U.S. on Saturday released photos of Ryan talking with Afghan elders and embracing a mourning man.

"We expressed our deepest condolences to the survivors of the noncombatants who were killed during this operation," Ryan said in a statement. "Our inquiry in Herat demonstrates how seriously we take our responsibility in conducting operations against militant targets and the occurrence of noncombatant casualties.

"Our concern is for the security of the Afghan people. To this end, we continually evaluate the operations we conduct during the course of our mission in Afghanistan and have agreed to coordinate our efforts jointly," Ryan said.

Holewinski said an upfront apology is what "U.S. and allied troops should have been doing from the beginning."

"Avoid harm, investigate when it occurs, apologize and provide compensation or other amends," she said.

After increasingly angry demands by Karzai for more U.S.-Afghan military cooperation, the American and Afghan militaries announced plans this month to increase the number of Afghans who will take part in U.S. operations.

The Afghan Defense Ministry condemned the civilian deaths in a statement Wednesday but noted it would take more time to implement the agreement. It also urged U.S. forces to "be very careful during their operations."

The investigative team's trip to Herat came one day after the U.N. released a report saying 2,118 civilians died in the Afghan war last year, a 40 percent increase over 2007 and the most in any year since the U.S.-led invasion in 2001 that ousted the Taliban's hard-line Islamist regime.

The report said U.S., NATO and Afghan forces killed 829 civilians, or 39 percent of the 2008 total. Of those, 552 deaths were blamed on airstrikes. Militants were blamed for 55 percent of the deaths, or 1,160.

President Barack Obama this week announced the deployment of 17,000 additional U.S. troops to Afghanistan to bolster the 38,000 already in the country to fight an increasingly violent Taliban insurgency. A higher number of troops in the country also means that civilian casualties could increase.

In Kabul, meanwhile, House Speaker Nancy Pelosi met with Karzai for talks about the ongoing American strategic review of the U.S. mission in Afghanistan, the president's office said.

Pelosi, D-Calif., arrived in Afghanistan on Friday to meet with Afghan officials and U.S. and NATO military leaders and troops, said Capt. Elizabeth Mathias, a U.S. military spokeswoman.

Afghanistan was to send a high-level delegation headed by Foreign Minister Dadfar Rangeen Spanta to the U.S. on Sunday "to review the joint strategy and the fight against terrorism," the Ministry of Foreign Affairs said Saturday.

Afghanistan's interior and defense ministers, its national security director and chief of intelligence are on the delegation.

Pakistan is also sending representatives. Spanta and Pakistan's foreign minister are expected to meet together with U.S. Secretary of State Hillary Clinton.