By Andrew Gray

WASHINGTON, June 8 (Reuters) - The Pentagon acknowledged on Monday that there were "problems" with the way U.S. forces conducted a bombing raid in Afghanistan that provoked outrage over civilian casualties.

Defense Secretary Robert Gates was briefed on the investigation into the incident, which took place in early May in the western province of Farah, a Pentagon spokesman said.

"There were some problems with some tactics, techniques and procedures or... the way in which close air support was supposed to have been executed in this case," said Pentagon press secretary Geoff Morrell, who sat in on the briefing.

The bombing heightened tensions between Afghans and foreign troops over civilian casualties. Afghan President Hamid Karzai has urged an end to U.S. air strikes in his country, but Washington has rejected his call.

Afghan officials put the civilian death toll from the Farah bombing as high as 140. An Afghan human rights watchdog put the total at 97 and said no more than two Taliban fighters were killed.

The U.S. military has said 20-35 civilians were among 80-95 people killed, most of them Taliban fighters who used the civilians as human shields.

Morrell said B-1 bomber, after identifying the targeted building, had to break off and then return to the scene to carry out the strike, without checking again whether the target was still appropriate.

There was no way to determine whether that had caused any civilian casualties, he said. "That was not part of the briefing that we received. It was just noted as one of the problems associated with these events, not that it was the cause of the civilian casualties."

Morrell said the investigation found that U.S. Marines on the ground took great care to limit civilian casualties.

He did not provide casualty figures, but said the civilian deaths were "greatly outnumbered" by the number of Taliban killed.

He declined to say whether the investigation, carried out by the U.S. military's Central Command, had found fault with any other part of the operation.

Morrell's remarks were the first public acknowledgment by the Pentagon of problems with the bombing operation. But last week military officials, speaking on condition of anonymity, confirmed a New York Times report that said the investigation had uncovered mistakes in the air strikes.

Central Command expects to release a summary of the investigation's findings later this week. (Editing by Chris Wilson)

AlertNet news is provided by