Hasan Kazemi-Qomi said the investigation should yield answers soon, but added that Iraqi vessels had crossed into Iranian waters.
Tehran initially denied reports of the naval skirmish, which occurred near the southern Iraqi city of Al-Basrah.
Iraqi President Jalal Talabani conceded ion 17 January that the Iraqi coast guard may have inadvertently strayed across the border.
The issue is being seen as a test case of relations between the two countries, which fought a war in the 1980s.
(compiled from agency reports)