Five security guards from Blackwater Worldwide have been indicted on charges related to a 2007 shooting in which 17 Iraqis were killed in a Baghdad square, two sources said Friday.
Members of the U.S-based Blackwater security firm scan Baghdad from a helicopter in 2005.
A sixth security guard is in plea negotiations, the sources told CNN.
The exact charges, handed up by a federal grand jury, aren't publicly known because the indictment is sealed. Prosecutors had been considering bringing such charges as murder and assault against the guards.
The charges could be made public as early as Monday. Defense attorneys for the men could not be reached for comment.
Iraqi authorities accused Blackwater guards of killing 17 civilians and wounding nearly 30 in the September 2007 shootings in Baghdad's Nusoor Square in western Baghdad.
Blackwater said at the time that its guards were acting "in response to a hostile threat," a statement repeated by company spokeswoman Anne Tyrrell in August.
Blackwater said its guards were protecting a U.S. diplomatic convoy when they came under fire.
But an Iraqi government commission that investigated the shootings accused the guards of firing on civilians indiscriminately. The first U.S. soldiers to arrive on the scene also told investigators they found no evidence the guards were fired upon, sources familiar with the investigation previously told CNN.
The incident heightened tensions between U.S. and Iraqi government officials and contributed to a protracted debate over the extent of immunity that U.S. military personnel and civilian contractors have from Iraqi laws.
Security contractors have had immunity from Iraqi law under a provision put into place in the early days of the U.S.-led occupation of Iraq. But starting next year, under a U.S.-Iraq security agreement that Iraq approved Thursday, Iraq will have the "primary right to exercise jurisdiction" over U.S. contractors and their employees.