The Pentagon said Tuesday it was launching a manhunt to find whoever leaked tens of thousands of classified documents on the war in Afghanistan, one of the largest security breaches in US military history.

US defense officials said the person behind the release of some 91,000 classified documents appeared to have "secret" clearance and access to sensitive documents on the Afghan war.

"We will do what is necessary to try to determine who is responsible," Pentagon press secretary Geoff Morrell said. "Until we know who's responsible, you have to hold out the possibility that there could be more information that has yet to be disclosed."

The documents, dating from 2004 to 2009, were released on whistleblower website Wikileaks on Sunday.

The most controversial allegations center around claims that Pakistan, a key US ally, allows its spies to meet the Taliban directly.

Afghanistan blamed its Western allies Tuesday for having an incoherent approach to insurgency.

"Having a contradictory and unclear policy towards those forces who have used terrorism as a tool of interference and destruction against others has had disastrous consequences," the National Security Council in Kabul said in a statement, referring to Pakistan.

However, Admiral Mike Mullen, the US military's top officer, denied Tuesday that information in the documents questioned US strategy or relations with Pakistan.

Mullen said he was "appalled" at the leak, but that the information had been taken into account during a strategy review last year and that Washington made clear to Islamabad its concerns about possible links to militant groups.

US relations with Pakistan have "dramatically" improved in the past year and Pakistan has launched offensives against Islamist extremists, Mullen added.

Meanwhile, those leaked files have become major fodder for the media.

Time magazine published a story of the top 10 leaks in US history on its website, ranking the last incident as No 1 on the table, ahead of the Watergate scandal's Deep Throat and The Treaty of Guadalupe Hidalgo Scandal.

Britan's The Guardian newspaper, one of the three media groups to have received the files from Wikileaks, published a section of spreadsheets showing explosive attacks against NATO forces and the number of soldiers killed in each attack. Some of the data is even downloadable on its website.