A cache of nearly 400,000 U.S. military documents from the Iraq War has indicated the existence of about 15,000 civilian deaths that were not previously documented, the publisher of the documents, WikiLeaks said Saturday.

The civilians died from a range of violent action, including targeted assassinations, checkpoint killings and sectarian violence, WikiLeaks and Iraq Body Count, a group that tracks civilian deaths from the war, told a news conference in London on Saturday.

The documents also show that the U.S. and the U.K. knew that Iraqi security forces were torturing Iraqis but declined to do anything about it, WikiLeaks and other panel members told the news conference.

Commenting on the allegation, Pentagon spokesman Marine Col. Dave Lapan said: "If our troops witness abuse or become aware of it they are obligated to take reasonable action to prevent observed abuse and report it to appropriate authorities…in Iraq, we regularly conducted human rights training with [Iraqi security forces] and saw their performance improve over time in this regard."

In a written statement, the U.K.'s Ministry of Defense said it would be "inappropriate to speculate on the specific detail of these documents without further investigation." It added that "there is no place for mistreatment of detainees and we investigate any allegation made against our troops. The protection of civilians is always at the core of what UK forces do in any operational theatre and any civilian casualty is, of course, a matter of deep regret."