His statement contradicts US accounts of the incident in Iraq in which Nicola Calipari was shot taking freed hostage Giuliana Sgrena to Baghdad airport.
Mr Berlusconi said the US must accept responsibility to restore relations.
He said his government had demanded “maximum co-operation” from the US, and a joint inquiry had been promised.
The US military in Iraq has begun an investigation led by Brig Gen Peter Vangjel into Friday’s shooting. It is expected to take up to four weeks to complete.