Rouhani's three-day visit comes as Iraq has been under pressure from Washington to limit ties with its neighbour, particularly after the United States withdrew from the Iran nuclear deal and hit Tehran with sanctions.
Iran has close but complicated ties with Iraq, with significant influence among its Shiite political groups.
Tehran dispatched "military advisors" and equipment overnight along with the famous Revolutionary Guards elite Qods Force commander Qasem Soleimani to prevent IS jihadists from approaching its western borders.
Following the defeat of IS in Iraq, Iran is trying to position itself to gain a prime role in rebuilding the war-ravaged country.
"Iran-Iraq relations are not comparable with (Iraq's relations) with an aggressor country like America," Rouhani said.
"America is despised in the region. The bombs that the Americans dropped on Iraqis, Syrian people and other countries cannot be forgotten and," he said.
Rouhani's visit to Iraq will be the first since he became president in 2013.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)