Al-Dabbagh said a probe ordered by Nuri al-Maliki, the Iraqi prime minister, found "no evidence that the Blackwater convoy came under any direct or indirect fire, or that it was even hit by stones".
Iraqis say civilians were killed without provocation by Blackwater guards on September 16.
On Sunday, a committee made up of US and Iraqi officials met for the first time to review the operations of foreign security firms in Iraq.
A US embassy statement said the joint commission, headed by Iraq's defence minister and a senior US diplomat, will put forward proposals to ensure that security firms guarding US officials "do not endanger public safety".
Blackwater employs 1,000 people in Iraq to protect US state department officials.
Iraq says there are more than 180 mainly US and European security companies in Iraq, with estimates of the number of private contractors ranging from 25,000 to 48,000.
Many Iraqis resent their presence, seeing them as private armies which have shot and killed civilians with impunity.
Condoleezza Rice, the US secretary of state, has ordered tighter controls on Blackwater including putting cameras on its convoys.
The state department also plans to send diplomatic security agents to accompany each convoy protected by Blackwater guards.