Pakistan was actively collaborating with the Taliban in Afghanistan while accepting US aid, new US military reports showed, a disclosure likely to increase the pressure on Washington's embattled ally.
Documents leaked by the organisation Wikileaks said representatives from Pakistan's Inter-Services Intelligence met directly with the Taliban in secret strategy sessions to organise militant networks fighting US soldiers.
The White House condemned the leak, saying it could threaten national security and endanger the lives of Americans. Pakistan said leaking unprocessed reports from the battlefield was irresponsible.
US national security adviser Jim Jones said the leak would not affect "our ongoing commitment to deepen our partnerships with Afghanistan and Pakistan".
The revelations were contained in more than 90,000 classified documents which US officials focused on the period leading to the launch of President Barack Obama's Afghan strategy last December, when he authorised deployment of 30,000 additional troops.
The founder of whistleblowing website WikiLeaks defended his decision to publish the secret US military files.
Julian Assange said it was clear that the course of the conflict needed to change, and that the newly released records would help to shape understanding of the past six years of fighting.
He claimed that the high level of civilian casualties reported in the files was in fact lower than the true figure because military personnel “downplayed” the number or reported them as insurgent deaths.
Speaking at a press conference at the Frontline Club in central London, Mr Assange brushed off the US administration’s criticism of the major leak. “We are familiar with groups whose abuse we expose attempting to criticise the messenger to distract from the power of the message,” he said.
“We don’t see any difference in the White House’s response to this case to the other groups that we have exposed. We have tried hard to make sure that this material does not put innocents at harm.
“All the material is over seven months old so is of no current operational consequence, even though it may be of very significant investigative consequence.”
Mr Assange added: “It’s clear that it will shape an understanding of what the past six years of war has been like, and that the course of the war needs to change. he manner in which it needs to change is not yet clear.”
The revelations emerged as Admiral Mike Mullen, chairman of the Joint Chiefs of Staff, warned of greater Nato casualties in Afghanistan as violence mounts over the summer.
It also came as the Taliban said they were holding captive one of two US servicemen who strayed into insurgent territory, and that the other had been killed. The reported capture will further erode domestic support for America's nine-year war.
Violence in Afghanistan is at its highest of the nine-year-old war as the thousands of extra US troops step up their campaign to drive insurgents out of their traditional heartland in the south.
"As we continue our force levels and our operations over the summer ... we will likely see further tough casualties and levels of violence," Admiral Mullen told reporters in Kabul yesterday.
The United States has repeatedly urged Pakistan to hunt down militant groups, including some believed to have been nurtured by the ISI as strategic assets in Afghanistan and against arch rival India. Islamabad says it is doing all it can to fight the militancy, adding it was a victim of terrorism itself.
Two US servicemen were reported missing on Friday after they failed to return in a vehicle they had taken from their compound in Kabul, the Nato-led force said.
A spokesman for the Nato-led force declined to comment on the Taliban's announcement it was holding one of the men, both from the US Navy.
The Navy described both men as still missing.
"We have the body of the dead soldier and the other one who is alive. We have taken them to a safe place," said Taliban spokesman Zabihullah Mujahid by telephone from an undisclosed location.
Rumours circulated in local and international media about the fate of the missing men and how they had managed to stray into an insurgent-controlled area in Logar province, a short but dangerous 100 km (60 miles) drive south of the capital. One provincial official said alcohol was found in their vehicle.
Last month was the deadliest for foreign troops since 2001, with more than 100 killed, and civilian deaths have also risen as ordinary Afghans are increasingly caught in the crossfire.
The only other foreign soldier believed held by the Taliban is Idaho National Guardsman Bowe Bergdahl, whose capture in June last year triggered a massive manhunt. His captors have issued videos of him denouncing the war, in what the US military has called illegal propaganda.
The leaked documents are available at http://www.wikileaks.org/wiki/Afghan_War_Diary,_2004-2010.