Afghans villagers sift through the rubble of destroyed houses after air strikes in Bala Baluk district of Farah province. (Associated Press)

U.S. Secretary of State Hillary Clinton expressed regret for any loss of life as Afghan President Hamid Karzai ordered an investigation Wednesday following allegations that more than 30 civilians died in a U.S.-led bombing.

"Any loss of life, any loss of innocent life is particularly painful," Clinton said in Washington, where she was meeting with Afghan and Pakistan officials.

Karzai thanked Clinton for "showing concern and regret."

In Afghanistan, the U.S. forces commander said it wasn't a certainty that the deaths happened as a result of American military action.

Gen. David McKiernan said American forces came to the aid of Afghans who may have been ambushed by the Taliban in Farah province on Sunday.

He said the Taliban beheaded three civilians, perhaps to lure police, and that the U.S. is working with the Afghans to learn the truth about the incident.

State Department spokesman Robert A. Wood said Clinton's remarks were offered as a gesture, before all the facts of the incident were known, because "any time there is a loss of innocent life we are going to be concerned about it, and we wanted to make that very clear."

Local officials in Bala Baluk said civilians died during bombing runs late Monday. Afghan officials and a U.S. brigadier-general are going to Farah province to investigate the incident, Karzai said in a written statement.

Rohul Amin, governor of Western Farah province, said it's believed that up to 100 civilians have been killed while provincial police chief Abdul Ghafar Watandar said the death toll could be even higher.

Karzai called any civilian casualties "unacceptable."

Karzai added he intended to raise the issue with U.S. President Barack Obama during a meeting in Washington on Wednesday.

Civilian deaths have caused increasing friction between the Afghan and U.S. governments, and Karzai has long pleaded with American officials to reduce the number of civilian casualties in their operations.

'Dozens of bodies'

Red Cross officials working in two villages in western Afghanistan have seen "dozens of bodies," said Jessica Barry, spokeswoman in Afghanistan for the International Committee of the Red Cross.

"There were bodies, there were graves, and there were people burying bodies when we were there," Barry said. The dead include women and children, she said.

A Red Crescent first aid volunteer was among the dead, Barry said.

Fighting broke out on Monday after Taliban fighters massed in Farah province, said Belqis Roshan, a member of Farah's provincial council.

At least 25 militants and three police officers died in that battle near the village of Ganjabad, Ghafar said.

Villagers in Ganjabad told Afghan officials they took children, women and the elderly to compounds nearby Gerani to keep them safe.

But there were conflicting reports that Taliban had used the civilians as shields and herded them into the compounds.

Fighter aircraft later bombed the compounds, killing a majority of those inside, villagers said.

A Western official in Kabul told The Associated Press that marine special operations forces had called in the air strike. The official asked not to be identified because he wasn't authorized to release the information.

At least 30 bodies

Villagers brought about 30 bodies, including women and children, to Farah city to show the province's governor on Tuesday, said Abdul Basir Khan, a member of Farah's provincial council.

Khan said villagers allege that more than 150 civilians died in the bombing. The claim has not been verified.

Mohammad Nieem Qadderdan, a former district chief of Bala Buluk, said between 100 and 120 people were killed in the attacks.

Villagers are still working to uncover the bodies, many of which are buried beneath the rubble of destroyed houses, Qadderdan said.

"We need more people to help us. Many families left the villages, fearing other strikes," he said.

Provincial authorities have told villagers not to bury the bodies, but instead to line them up for the officials conducting the investigation to see, Qadderdan said.

"Taliban fighters fought Afghan and foreign troops yesterday and the day before but the casualties from last night's bombings were all civilians," Taliban spokesman Qari Yousuf Ahmadi told the Reuters news agency.

Officials have also not yet been able to confirm if any militants are believed to be among the dead.

With files from The Associated Press