Pakistan was working with the Taliban in Afghanistan to organise militant attacks on US soldiers, according to documents released by whistleblowing website Wikileaks on Monday.
The site published leaked military reports detailing American fears that their ally was undermining their efforts to stabilise the country.
The White House called the move irresponsible, saying that it will put the lives of US troops at risk.
But the founder of Wikileaks defended the decision to publish in what is one of the largest unauthorised disclosures in military history.
“It’s clear that it would shape an understanding of what the past six years of war has been like and that the course of the war needs to change,” Julian Assange told reporters in London.
“The manner of it needs to change it’s not yet clear,” he said.
The documents, dubbed the Afghan War Diaries, say Pakistani agents held talks with Taliban insurgents with a view to orchestrating attacks on US forces.
They also outline previously unreported civilian casualties and what Assange said amounts to evidence of war crimes.
Senior military officials have hit out at the website for putting the reports online.
“I don’t think that Wikileaks putting this kind of information in this raw context on the Internet is responsible at all,” said Richard Kemp, a former British commander in Afghanistan.
“I think that is quite the reverse. It doesn’t actually help anybody in understanding the war to any great extent. It won’t change the course of the war. It potentially could endanger British lives and it will aid the Taliban in what they trying to do,” Kemp said.
Pakistan has strongly denied the claims made in the leaked documents and has reaffirmed its commitment to helping its US ally win the war against the Taliban.