"We will do what is necessary to try to determine who is responsible for the leaking of this information," 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. And that's obviously a concern," added Morrell.
Over 90,000 classified documents were leaked to the whistleblowers' website, WikiLeaks, on Sunday, Jul 25 evening. The documents exposed the details on the death of thousands of civilains in the military operations by the coalition troops, surge in Taliban attacks and the fears of NATO that Pakistan and Iran were fuelling insurgancy.
US defence officials suspect that the person behind the leak may have "secret" clearance and access to sensitive documents on the Afghan war.
The Pentagon is currently reviewing the documents. It said that the process would take "days if not weeks" and that it was too soon to assess any damage to national security.
"The scale of (the leak), the scope of it, is clearly alarming. I don't think the content of it is very illuminating," Morrell said.
To a question if WikiLeaks would face any repurcussions, the Pentagon official said, "I don't know what's going to happen here. This is a whole new world that we are entering into where an organisation without any editorial judgment, beholden to nobody, is soliciting classified information from people all over the world and then publishing it.
"I don't know. I'm not a lawyer but people are going to have to make judgments about whether there are legal ramifications for soliciting a criminal act."