Iranian Foreign Minister Mohammad Javad Zarif has begun a two-day visit to Iraq.
Iraq is fighting a Sunni Muslim insurgency led by Islamic State jihadists.
He was due to meet his Iraqi counterpart Hoshyar Zebari as well as the prime minister-designate, Haidar al-Abadi, with the issue of the Iran-Iraq border demarcation also on the agenda.
Iran, which like Iraq is predominantly Shia, was a longtime backer of the outgoing premier, Nuri al-Maliki, before dropping its support of the divisive leader in favour of Abadi.
The Iranian government has called for Iraqi parties to unite in the face of the Islamic State which has seized large swathes of the country.
Iran says it is providing advice to Iraqi Kurds fighting the jihadists.
France, meanwhile, has pressed "all countries in the region" including Iran to join Western nations in the fight against the IS, which is also rampaging through Syria.