Assange sent out an email to his supporters saying that WikiLeaks would publish a May 2009 video showing the air attack on the village of Garani, where people were celebrating a wedding. Some 140 people died, including women and children. The deaths were characterised as the largest civilian loss of life since the US invasion in 2001.
Assange has gone into hiding, cancelling public appearances, after US authorities said they would like to speak to him regarding a previous leaked video that was posted on the WikiLeaks website and went viral.
The classified Pentagon video shows a 2007 American helicopter attack in Baghdad, which killed 12, with accompanying audio providing a chilling commentary.
The alleged video leaker is 22-year-old army specialist Bradley Manning, who is currently being held in Kuwait.
"It is a safe bet that NSA (National Security Administration), CIA, FBI and other agenies have been instructed to do all possible to make an example of the WikiLeaks leader, australian-born Julian Assange, and his colleagues. Much as at stake-- for both the Pentagon and freedom of the press," said a letter signed by Coleen Rowley, an FBI whistelblower and one of Time Magazine's People of the Year 2002, Ray McGovern, a veteran CIA analyst and Daniel Ellsberg, who leaked the Pentagon Papers about governmental deceit during the Vietnam War.
Manning is also accused of sending some 260,000 classified documents to WikiLeaks. Assange said he does not have 260,000 documents, and refuses to name Manning as the source.
"We have denied the allegation, but the US government is acting as if the allegation is true and we do have a lot of other material that exposes human rights abuses by the United States government," said Assange in an email.
US officials would like to speak to Assange about these documents, however, and the Iraq video that was posted and the Afghan video that he plans to post.