The United States is concerned about a coming dump of classified documents by WikiLeaks, expected to be diplomatic cables, State Department spokesman Philip Crowley said Wednesday.

"We are in touch with our posts around the world. They have begun the process of informing governments that a release of documents is possible in the near future," Crowley said.

"This is going to be unhelpful."

Crowley said that WikiLeaks release of classified documents, is "harmful to our national security. It does put lives at risk. It does put national interests at risk."

He said that diplomatic cables, messages between US posts around the world, "involve discussions that we had with government officials, with private citizens."

"Inherent in this day-to-day action is trust that we can convey our perspectives to other governments in confidence," he said. Breaking that confidence "has a impact."

"These revelations ... are going to create tensions on our relationships between our diplomats and our friends around the world," he said.

WikiLeaks has not said what will be contained in its coming release, indicating only that it will be "seven times" the Iraq War logs in which it posted 400,000 secret documents.

A new posting would mark WikiLeaks' third mass release of classified documents after it published 77,000 secret US files on the Afghan conflict in July.

WikiLeaks argues the release of the documents, US-soldier authored incident reports from 2004 to 2009, has shed light on the wars, including allegations of torture by Iraqi forces and reports that suggested 15,000 additional civilian deaths in Iraq.

WikiLeaks' announcement Monday came just days after Sweden issued an international arrest warrant for the website's head, Australian national Julian Assange, wanted for questioning related to rape and sexual molestation accusations.