President Hassan Rouhani's visit to Iraq this week is a strong message to the United States and its regional allies that Iran still dominates Baghdad, a key arena for rising tension between Washington and Tehran.
The first Iranian presidential visit to Iraq since 2013 is also meant to signal to President Donald Trump's administration that Tehran retains its influence in much of the region despite US sanctions.
"Iran and Iraq are neighbours and no country can interfere in their relations," Foreign Minister Mohammad Javad Zarif said after arriving in Baghdad to prepare for the visit.
Rouhani's three-day trip starting on Monday includes meetings with Iraq's president and prime minister, tours of Shia Muslim holy sites and a meeting with top Iraqi Shia cleric Grand Ayatollah Ali al-Sistani, Iranian state media reported.
Rouhani made clear last week the debt he believes Baghdad owes Tehran for support in the battle to defeat Daesh. Iranian forces and the militias they back played a crucial role defeating Daeshin Iraq and Syria.
In comments published on his official website, he said:
If the support of the Islamic Republic of Iran didn't exist then Baghdad and the Kurdistan region would have definitely fallen and Daesh would dominate the region
Iran mostly relies on other senior officials to conduct its dealings with Iraq, with which it shares an almost 1,500 kilometre (900 miles) long border. Most prominent of these has been Revolutionary Guards commander Qassem Suleimani, who was instrumental in directing the battle against Daesh in Iraq and Syria.
But as it tries to counter the pressure from US sanctions, Iran is seeking to shore up its political and economic influence along a corridor of territory it effectively controls from Tehran to the Mediterranean through Iraq, Syria and Lebanon.
"Tehran and its allies in Baghdad and Damascus achieved victory in the war against the Daesh but the Islamic Republic risks losing the peace," said Ali Alfoneh, senior fellow at the Arab Gulf States Institute in Washington.
"Apart from Russian companies, UAE companies are aggressively trying to gain a foothold in Iraq and Syria, which would deprive Iranian companies of reaping the fruit of their war era effort."
Iran's influence in Iraq will be difficult to dislodge, however. Through allied Iraqi politicians and paramilitary groups, it emerged as the dominant force after the US-led invasion that toppled Saddam Hussein in 2003.
Iran officially has no military presence in Iraq but backs its most powerful Shia paramilitary groups. An umbrella grouping of all Iraq's Shia militias is estimated at 150,000 fighters.
Last week Washington blacklisted another Iran-backed militia that has helped create a supply route through Iraq to Damascus. The United States has around 5,200 troops stationed in Iraq.
Tehran also has powerful allies in Iraq's parliament whose attempts to pass a bill forcing US troops to leave the country might be aided by Trump's belligerent anti-Iran rhetoric – especially comments roundly derided by Iraqi leaders that US forces in Iraq, ostensibly there for the battle against Daesh, can be used to "watch Iran".