The whistleblower has also alleged that the murders of the Royal Military Policemen, more than 10 years ago, were part of a series of attacks backed by Iran.
Corporals Russell Aston, 30, Simon Miller, 21, Lance Corporal Benjamin McGowan Hyde, 23, and Lance Corporal Tom Keys, 20, Sergeant Simon Hamilton-Jewell, 41, and Corporal Paul Long, 24, were killed when a 400-strong mob descended on a police station in Majar al-Kabir in June 2003, in a region that was deemed particularly hostile.
Lawyer Simon McKay, acting on behalf of four of the families, has asked the Ministry of Defence (MoD) to investigate the new claims.
In a letter to the MoD, Mr McKay said: "We have been made aware from a senior retired army officer who was serving in Iraq at the time of this incident that the authorities had received intelligence prior to the events on June 24 2003 that there would be an escalation in violent attacks in the Al Majar region.
"The intelligence was of a sensitive nature provided by the general communications officer. It assessed the violence was sponsored by Iranian-backed interests."
The families of Cpl Aston, Cpl Miller, Cpl McGowan Hyde and Cpl Keys, those represented by Mr McKay, are bringing a human rights act claim against the MoD.
They hope their legal action against the MoD will trigger a public inquiry into the deaths, having said they were dissatisfied with both the inquests and board of inquiry investigation which followed the deaths.
Mr McKay says the action "will allege that the state failed to provide sufficient procedural safeguards to ensure the deaths of their sons were either avoidable or that following their deaths there was an effective and independent investigation into the circumstances".
The MoD said no practical purpose would be served by a public inquiry.