WASHINGTON (Reuters) - A U.S. military investigation has found American and Afghan commandos wrongly concluded there were no Pakistani forces in a border area where an air strike killed 24 Pakistani troops last month, the Wall Street Journal reported on Thursday.

The investigation, due to be presented to U.S. defense officials on Friday, acknowledges significant U.S. responsibility for the November 26 air strike that deepened mistrust between the United States and Pakistan, the Journal said, citing unidentified U.S. officials familiar with the report.

The uneasy allies faced a series of crises in the past year, including the U.S. raid that killed al Qaeda leader Osama bin Laden on Pakistani soil in May, the closure of NATO supply routes through Pakistan, and the arrest of a CIA contractor.

The U.S. military report supports some main elements in Pakistan's version of events and conflicts with early U.S. accounts that said Pakistanis gave an all-clear before what would become the most deadly friendly-fire accident of the war in Afghanistan, the newspaper said.

"The overarching issue that surrounds this incident is a lack of trust" between the United States and Pakistan that led to the incident, the Journal quoted a military official as saying.

The air strike incensed the Pakistanis, who demanded that the United States leave the Shamsi Air Base within 15 days and blocked ground supply routes through Pakistan to U.S. forces in Afghanistan. They also want a formal U.S. apology.

According to the newspaper, the U.S. report says a U.S.-Afghan commando team came under attack from positions along a ridgeline, after which an F-15 fighter jet and AC-130 gunship launched warning flares towards the positions high above the commandos.

Forces on the ground asked NATO for a report on the area, the Journal reported, and were told in a radio transmission: "We are not tracking any pak mil in the area." The ground forces interpreted that to mean there was no Pakistani military there, a military official familiar with the report told the Journal.

A second mistake involved inaccurate data provided by the U.S. forces to the Pakistani military at a border coordination centre, the report said.

However U.S. military officials said Pakistani forces should have realized they were not firing on insurgents because of the fighter jets and gunships, the newspaper reported.

"It's hard to mistake these units for insurgents," a U.S. official told the Journal. "One of the gaps in this investigation is we don't know why they came under fire by the Pakistani military."

Mochila insert follows.