U.S. military officials failed to investigate hundreds of reports of abuse, torture, rape and murders, according to classified documents examined by the Guardian, a British newspaper.

The documents cited by the Guardian said that as recently as December 2009, U.S. authorities were passed a video of Iraqi soldiers executing a bound detainee.

The documents, given to the Guardian and the New York Times by WikiLeaks, also indicate that as far back as 2005, Iran armed and trained squads to kill senior Iraqi politicians and undermine U.S. and British military operations, the Guardian reported. Der Spiegel of Germany and France's Le Monde also were given advance copies of almost 400,000 documents generated between 2003 and 2010 by U.S. military units.

WikiLeaks.org receives confidential material that governments and businesses want to keep secret and posts the information on the Internet. The group plans a news conference in London tomorrow.

The U.S. Defense Department "strongly" condemns the unauthorized release of the documents, spokesman Geoff Morrell said in an e-mailed statement. Morrell declined to comment on the documents themselves, other than to call them initial, raw observations by tactical units.

The documents indicate that the number of Iraqi civilians killed was greater than the U.S. revealed during the Bush administration, according to the New York Times. While the documents don't give a precise count, they list more than 100,000 deaths over five years ending in 2009, with some incidents counted twice or inconsistently, the newspaper said.

Mistreatment of Iraqi prisoners by their own forces appeared to be even more graphic than the accounts of abuse by the U.S. military at the Abu Ghraib prison, the Times said. The documents contain references to at least six prisoners who died in Iraqi custody during the six years covered as well as hundreds of accounts of beatings, burnings and lashings.

A Pentagon spokesman said international practice makes Iraqi authorities responsible for investigating abuses by their own forces, the Times said.

Release of the information poses a risk to U.S. national security and relations with Iraq, Pentagon spokesman Colonel David Lapan told reporters earlier today. He said the documents might identify Iraqis who worked closely with the U.S.

"Our concern is the threat to individuals, our people and our equipment," he said. "But in terms of the insight captured -- incidents of innocent Iraqis killed, detainee abuse -- all of those things have been very well chronicled. Iraq is still trying to form a government."

Releasing the material is a "hugely irresponsible step on the part of WikiLeaks," Ryan Crocker, a former U.S. ambassador to Iraq, told a forum at the Center for Strategic and International Studies in Washington today.

"I'd really be worried if, as looks to be the case, you have Iraqi political figures named in a context or a connection that can make them politically and physically vulnerable to their adversaries," said Crocker, who is now dean of the Bush School of Government and Public Service at Texas A&M University in College Station.