The White House accused online whistleblower WikiLeaks of endangering the lives of American, British and other coalition troops after it posted around 90,000 leaked US military records today.
The documents amount to a blow-by-blow account of six years of the Afghanistan war, including unreported incidents of Afghan civilian killings as well as covert operations against Taliban figures.
The White House condemned the document disclosure, saying it "put the lives of Americans and our partners at risk".
The documents, including classified cables and assessments between military officers and diplomats, also describe US fears that ally Pakistan's intelligence service was actually aiding the Afghan uprising.
The documents, dated between January 2004 and December 2009, are largely what is called "raw intelligence" - reports from junior officers in the field that analysts use to advise policymakers.
White House national security adviser General Jim Jones stressed that the documents described a period from January 2004 to December 2009, during the administration of President George Bush.
That was before "President Obama announced a new strategy with a substantial increase in resources for Afghanistan, and increased focus on al-Qa'ida and Taliban safe havens in Pakistan, precisely because of the grave situation that had developed over several years", he said.
The New York Times said the documents suggested Pakistan "allows representatives of its spy service to meet directly with the Taliban in secret strategy sessions to organise networks of militant groups that fight against American soldiers in Afghanistan, and even hatch plots to assassinate Afghan leaders".
General Jones praised a deeper partnership between the US and Pakistan, saying: "Counter-terrorism co-operation has led to significant blows against al Qaida's leadership." Nevertheless, he called on Pakistan to continue its "strategic shift against insurgent groups".
German magazine Der Spiegel reported that the records showed Afghan security officers as helpless victims of Taliban attacks.
It said the documents showed a growing threat in the north, where German troops were stationed.
While the documents provide a glimpse of a world the public rarely sees, the overall picture they portray is already familiar to most Americans.
US officials have already publicly condemned Pakistani officials' co-operation with some insurgents, like the Haqqani network in tribal areas.
The success of US special operating forces teams at taking out Taliban targets has been praised by US military and intelligence officials.
And newly-resigned General Stanley McChrystal, who was leading the Afghan war effort, made protecting Afghan civilians one of the hallmarks of his command, complaining that too many Afghans had been accidentally killed by Western firepower.
One US official said the Obama administration had already told Pakistani and Afghan officials what to expect from the document release, in order to head off some of the more embarrassing revelations.
Another US official said it may take days to comb through all the documents to see what they mean to the US war effort and determine their potential damage to national security. The official added that the US was not certain of the source of the leaked documents.
US government agencies have been bracing for the release of thousands more classified documents since the leak of a classified helicopter cockpit video of a 2007 firefight in Baghdad. That leak was blamed on a US Army intelligence analyst working in Iraq.
Spc Bradley Manning, 22, of Potomac, Maryland, was arrested in Iraq and charged earlier this month with multiple counts of mishandling and leaking classified data, after a former hacker turned him in.
Manning had bragged to the hacker, Adrian Lamo, that he had downloaded 260,000 classified or sensitive US State Department cables and transmitted them by computer to Wikileaks.org.
Lamo turned Manning in to US authorities, saying he could not live with the thought that those released documents might get someone killed.