The US military says it has detained four more Iraqi men suspected of shooting down a commercial helicopter earlier this week.
Bulgarian sources say the helicopter was brought down by a missile
Six US security contractors, three Bulgarian crew members and two Fijian security guards died when the Bulgarian aircraft crashed just north of Baghdad.
On Saturday, six other men were apprehended in connection with the attack after a tip-off from a civilian.
US officials said bomb-making material was also seized during the raids.
"In the last 24 hours, the number of captured terrorists suspected to have possible links to the shooting down of a civilian Mi-8 helicopter has increased to 10," the US military said in a statement.
Earlier it said the civilian was crucial to helping to apprehend the first six suspects.
"The Iraqi citizen told the soldiers he knew where the blue pick-up truck the terrorists used during the attack was parked and led them to the site," it said in a statement.
"When the soldiers got there, several other local residents confirmed the first tip and showed the soldiers where the terrorists lived."
No further information was released on the identities of the men, or the locations of the arrests.
A leading insurgent group, the Islamic Army in Iraq, said it carried out the attack, the first of its kind on a civilian aircraft in Iraq.
Video footage shown by al-Jazeera television indicated that a Bulgarian crew member survived the crash, only to be shot dead by militants scouring the wreckage.