"That said, prima facie, there does appear to be evidence of war crimes in this material."
The US government criticised the publication of the material and said it could threaten national security.
The Pentagon said that the documents would be reviewed in order to "determine the potential damage" to the lives of troops and coalition partners.
However, the review is expected to take "days, if not weeks" to complete.
Nato's European members said they hoped the leaked documents would not negatively affect the current war effort.
"We are working hard with our allies on improving security on the ground and increasing ... the capacity of the Afghan government, so we are not going to spend our time looking at leaks," William Hague, the British foreign secretary, said.
Pakistan's Inter-Services Intelligence (ISI) agency lashed out against allegations that close connections existed between it and the Taliban in Afghanistan.
The ISI said the allegations, which have been repeated for years, are unsubstantiated.
The documents raised new questions about whether the US can succeed in convincing Pakistan to sever historical links to the Taliban and deny them sanctuary along the Afghan border.
They appeared to show Pakistan collaborated with the Taliban while accepting US aid.
A senior ISI official denied the allegations and said that they were from raw intelligence reports that had not been verified.
Assange said the power of the material lay in its accumulation of small, previously unknown details from the war in Afghanistan, rather than any disclosure of one large event.
He did not however reveal the source of the leak.
"The real story of this material is that it is war, it is one damn thing after another. It is the continuous small events, the continuous deaths of children," Assange said.
Haroun Mir, a director with Afghanistan's Centre for Research and Policy Studies, told Al Jazeera that "is not a big surprise".
"When it comes to the Pakistani support for the insurgents in Afghanistan, we Afghans have been talking about this for a long time."
Mir said that Hamid Karzai, the president of Afghanistan, "raised this issue several times with US and Pakistani officials, but unfortunately we never had any positive feedback from the US".
"I think its time for the US administration to explain to their own public and the US congress about why they tried to hide these reports for such a long time."