Afghanistan war logs: Wikileaks founder rebuts White House criticism

He said the files showed that "thousands" of war crimes may have been committed in Afghanistan.

The documents have revealed unreported incidents of Afghan civilian killings and information about secret operations against Taliban leaders, as well as highlighting US fears that Pakistan's intelligence service was aiding the Afghan uprising.

Assange rejected accusations that the leak had compromised America's national security. "We are familiar with groups whose abuse we expose attempting to criticise the messenger to distract from the power of the message."

"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."

Speaking at a press conference at the Frontline Club in central London, Assange said that the 90,000 leaked US military documents about the war in Afghanistan would help shape understanding of the past six years of fighting.

On the question of whether crimes had been committed, he said: "It is up to a court to decide clearly whether something is in the end a crime. That said, on the face of it, there does appear to be evidence of war crimes in this material."

Earlier, the White House said the leaks "could put the lives of Americans and our partners at risk, and threaten our national security".

It said that Wikileaks had made no effort to contact US security services, but insisted that what it called the "irresponsible leaks" would not "impact our ongoing commitment to deepen our partnerships with Afghanistan and Pakistan; to defeat our common enemies; and to support the aspirations of the Afghan and Pakistani people".

In London, the security minister Lady Neville-Jones, former chair of the UK's joint intelligence committee, described the leak as "really serious stuff" and questioned how the documents had been obtained.

"We don't know how they got that material – it may be a combination of leaking of documents, but also one strongly suspects they have hacked into systems as well.

"This is a very, very big story. But if you stop to think about it for a moment, military systems have to be secure because people's lives are at stake."

The Guardian, along with the New York Times and German weekly Der Spiegel, were given access to the archive and have spent several weeks investigating the logs. In order not to compromise intelligence sources or to put forces at risk, the Guardian has only published a selection of the logs, relating to significant events.

The White House national security adviser, General Jim Jones, stressed that the documents related to a period from January 2004 to December 2009, during the administration of President George Bush and before President Obama ordered a "surge" in Afghanistan.

"President Obama announced a new strategy with a substantial increase in resources for Afghanistan, and increased focus on al-Qaida and Taliban safe havens in Pakistan, precisely because of the grave situation that had developed over several years," he said.

Labour leadership candidate David Miliband, said the "war logs" showed that the war could not be won by military means alone.

"We cannot kill our way out of an insurgency. Instead, the battle for power is fought in the minds of the local population, insurgents and western publics. The purpose of military effort and civilian improvement is to create the conditions for political settlement.

"There is now a race against time to persuade the Afghan people that the correct strategy is in place and show our own people it can succeed. Better Afghan security forces, better police, better schooling and economic opportunities are all vital but not enough. None of them are durable or possible without a political settlement."

Miliband, the former foreign secretary, said any peace settlement "must include the vanquished as well as the victors" and urged the government in Kabul to involve Afghans in "defining a political endgame".

Elsewhere, experts analysed the damage inflicted on the war effort by the leak. British military expert professor Michael Clarke, director of the Royal United Services Institute thinktank, said the leaked files were less damaging than the Abu Ghraib Iraqi prisoner abuse scandal but would prove awkward for politicians.

"There is no doubt that the leaks are politically pretty damaging. The papers give an impression of a lack of military discrimination in how operations were conducted. They are also appearing at the worst possible time, particularly in the United States, because people are looking for an exit strategy. This is old bad news at a new bad time."

In the US, the chairman of the Senate foreign relations committee and former Democrat presidential candidate, John Kerry, responded to the leak with a direct challenge to the administration. "However illegally these documents came to light, they raise serious questions about the reality of America's policy toward Pakistan and Afghanistan," he said.

"Those policies are at a critical stage and these documents may very well underscore the stakes and make the calibrations needed to get the policy right."