Those documents included descriptions of attacks on Iraqi security forces and U.S. forces, detainee abuse, civilian casualty incidents, IED blasts, discussions with Iraqis and inquiries into socio-political relations, according to Department of Defense spokesman Col. David Lapan.
Sources that saw the WikiLeaks documents in advance reported no major revelations, but said taken together they could be read as a secret history of the war written from a troop's-eye-view of the conflict.
WikiLeaks collectively referred to the trove as "The Iraq War Logs" and seemed to suggest they did contain revelations.
"There are reports of civilians being indiscriminately killed at checkpoints, such as speeding to get a pregnant woman to hospital; of Iraqi detainees being tortured by coalition forces; and of U.S. soldiers blowing up entire civilian buildings because of one suspected insurgent on the roof," WikiLeaks said in its statement.
"There are over 300 recorded reports of coalition forces committing torture and abuse of detainees across 284 reports and over 1,000 cases of Iraqi security forces committing similar crimes," WikiLeaks added. "There are numerous cases of what appear to be clear war crimes by U.S. forces, such as the deliberate killing of persons trying to surrender."
The documents also included evidence of state-sanctioned torture by the Iraqi government, new evidence of Iraqi government death squads, and Iran's involvement in funneling arms to Shiite militias, according to the international news outlets that reviewed them before their release.
ABC News did not begin to review the nearly 400,000 documents firsthand until after their release this evening.
As the details on the documents emerged, the main WikiLeaks site was down for "scheduled maintenance," but the 400,000 documents later could be searched by categories on a specially created Wikileaks page.
WikiLeaks said it would hold a press conference Saturday morning in Europe to elaborate on the documents.
WikiLeaks' release comes at a critical time, as U.S. troops begin a staged withdrawal from Iraq. All 50,000 remaining U.S. troops in the country are expected to leave by the end of next year.
As occurred with the Afghanistan documents, the Iraqi war documents were initially thought likely to contain the names of Iraqis who cooperated with U.S. forces -- though it was not immediately clear if such names survived WikiLeaks redaction effort.
In July, WikiLeaks published a raft of secret documents from Afghanistan that the website obtained from a single rogue soldier, Army Spc. Bradley Manning, who had access to secret intelligence contained on military computers.
Among the documents Manning leaked was a classified video showing an Apache helicopter attack in 2007 that killed civilians and two Reuters news photographers. Manning is currently in a military brig near Washington, D.C., awaiting a court martial.
The Afghanistan documents contained the names of locals who cooperated with U.S. forces, and it was expected the Iraqi war documents likely would contain such names, as well.
The Pentagon has continued to express concerns about WikiLeaks releasing unredacted information containing such names because of the potential harm the individuals might face from insurgents.
"Our concern is mostly with the threat to individuals, the threat to our people and our equipment," said Lapan.