Washington has notified Ottawa that the WikiLeaks secret-spilling website is about to release some sensitive U.S. diplomatic files that could damage U.S. relations with allies around the world.

U.S. officials say the documents could be released this weekend or early next week. They say the internal documents may contain accounts of compromising conversations with political dissidents and friendly politicians and could result in the expulsion of U.S. diplomats from foreign postings.

Walter Dorn, an associate professor at the Royal Military College of Canada, said the leaked documents could "provide a window into the diplomatic exchanges with Canada and a frank view of how Canadian officials are viewed by the U.S. ambassador and by officials in the U.S. embassy.

They may also "show us how the U.S. tried to keep Canada in Afghanistan," Dorn added.

American officials are concerned that details about certain sensitive programs could be exposed, or details about surveillance at U.S. diplomatic compounds abroad.

The U.S. ambassador to Canada David Jacobson has already phoned Minister of Foreign Affairs Lawrence Cannon to inform him of the matter, the Foreign Affairs department says.

Foreign Affairs spokesperson Melissa Lantsman tells The Canadian Press the Canadian Embassy in Washington is "currently engaging" with the U.S. State Department on the matter.

The State Department said Wednesday that it had begun notifying foreign governments that WikiLeaks is preparing to release sensitive U.S. diplomatic files that could damage U.S. relations with friends and allies across the globe.

"These revelations are harmful to the United States and our interests," State Department spokesman P.J. Crowley said. "They are going to create tension in relationships between our diplomats and our friends around the world."

WikiLeaks itself has not said what will be contained in its coming release. On its Twitter feed earlier this week, the website said its next release would be "seven times larger" than the 400,000 Pentagon reports related to the Iraq war that it made public in October.

Crowley said the State Department "has known all along" that WikiLeaks possesses classified State Department documents.

He said the State Department does not know which files will be released so it was not possible to predict the impact of their release.

"We wish this would not happen, but we are obviously prepared for the possibility that it will," he added.

It's possible the documents with reveal the kinds of pressure the administration of President Barack Obama has put on various countries to accept the transfer of Guantanamo Bay detainees.

Canadian detainee Omar Khadr was the subject of discussions last month between Cannon and U.S. Secretary of State Hillary Clinton.

Canada has long resisted repatriating Khadr, the only western detainee remaining at Guantanamo Bay. That position is thought to have caused tensions between the two countries.

The posting will mark WikiLeaks' third mass release of classified documents after it published 77,000 secret U.S. files on the Afghan conflict in July.

With files from the Associated Press