Rubaie said the attack in Samarra, north of Baghdad, had been intended "to drive a wedge between Shiites and the Sunnis and to create a sectarian war."
Thousands of Shiites and Sunnis have died in tit-for-tat killings in the aftermath of the bombing of the mosque, the burial place of two Imams revered by Shiites.
Rubaie said the mastermind of the Samarra attack, Iraqi Haitham al-Badri, was linked to the previous regime before joining Ansar as-Sunna and ultimately Al-Qaeda. He said Badri remains at large.
The US military announced Thursday the death of two servicemen, bringing its overall toll in Iraq since the invasion to 2,523, according to an AFP count based on Pentagon figures.
And in rebel violence Thursday, four people, including the chief of security for Baghdad University, were killed in Iraq.