"We insisted that Iran be present. However, it's not us that took the decision. We regret the absence of Iran at this conference," Ibrahim al-Jaafari told reporters.
"All countries are affected by the Daesh (IS) problem and Iran is a neighbouring country that has several times given us its support," added the minister.
An elite unit of Iran's Revolutionary Guards, the Qods Force, and allied militias are reportedly on the ground in Iraq fighting IS. Iran, like Iraq, is majority Shiite, while IS is made up of Sunni fighters who target Shiite Muslims.
"We didn't go into details this morning. The different parties all had positive reactions concerning the current situation and the support they will give to Iraq," he said.
More From This Section
Some 30 countries and international organisations took part in the Paris conference. They agreed to support Iraq in its fight against IS jihadists by "any means necessary", including "appropriate military assistance".
Jaafari said the "liberation" of the northern city of Mosul from the extremists was a "strategic objective" of Baghdad and voiced optimism that it could soon be retaken.