Iraq's invasion of Iran in the 1980s sparked a near decade-long war that cost millions of lives.
Since the fall of Saddam a year ago, the Iranian government has frequently expressed its readiness to participate in rebuilding Iraq. But U.S. officials repeatedly accuse Iran of interfering in Iraq's affairs.
Speaking yesterday, U.S. Defense Secretary Donald Rumsfeld said: "We know the Iranians have been meddling [in Iraq] and it is unhelpful to have neighboring countries meddling in the affairs of Iraq, and I think the Iraqi people are not going to want to be dominated by a neighboring country, any neighboring country. No country wants to be dominated by its neighbors."
Analysts have widely differing views on Iran's intentions in Iraq.
Davoud Hermidas Bavand is a professor of international law in Tehran. Bavand sees Iran's influence as largely positive.
"Iran's intention is developing a neighborly relationship with Iraq in different areas in economic and commercial term as well as in political context," Bavand said.
Bavand added that the two countries should settle several open issues relating to the war, such as compensation and border issues.
Michael Rubin, a resident fellow at the right-leaning American Enterprise Institute, a Washington policy institute, recently returned from eight months in Iraq. He sees things differently.
"I believe the Iranians have bad intentions with regard to Iraq,” Rubin said. “Of course, Iran wanted to see Saddam Hussein gone, but they don't want to see a stable democratic country on their border all the more so because if the clerics in Iraq have freedom of speech then [they] can challenge the religious legitimacy not just the political legitimacy of the Iranian hierarchy."
Other observers say Iran does not have a consistent policy toward Iraq. Various groups are said to have different agendas, while the government has pursued closer ties in some specific policy areas.
Alireza Nourizadeh is a London-based journalist and the director of the Center for Arab-Iranian Studies (CAIS). Nourizadeh said, indeed, different factions in Iran have different aims.
"We have to consider the different factions with their own agendas in Iraq -- for instance the so-called conservatives. They do not want to see a secular state in Iraq. The reformers, of course, want the Iraqi experience to end with success because they believe that if there is a democratic government in Iraq at the end of the day it's going to help their status in Iran and it's going to help them to have more influence in the power struggle," Nourizadeh said.
Some observers say Iran is playing a double game in Iraq, being helpful in some areas while causing problems in others. Bavand, however, said ultimately a stable and peaceful Iraq is in Iran's interest.
"That's possible, but I do not think it's the general policy of the government as a whole. There is no doubt in Iran there are different factions which assume different positions regarding Afghanistan and possibly in Iraq, but if we take into consideration the general position or a strategy of a country, I do believe Iran has no choice but to adapt a positive view toward the socio-political situation in Iraq and work out for the better relationship with the future government of Iraq," Bavand said.
The U.S.-led Coalition Provisional Authority -- which heads Iraq's interim government -- appears wary of expanding religious ties between Iraq and Iran. Iran is a Shi’a Muslim state -- the same sect of Islam shared by around 60 percent of Iraq's population. The next government in Baghdad will most probably be controlled by Shi’as.
Added to that, the U.S. is now struggling to contain a deadly Shi’a insurgency in parts of the capital Baghdad, as well as in the south and east of the country.
Some reports have gone so far as to accuse Iran of actively supporting the leader of the insurgency, Shi’a cleric Muqtada al-Sadr. Al-Sadr is a follower of Ayatollah Kazem al-Haeri, a conservative cleric based in Iranian religious center of Qom. Al-Sadr visited Iran in June and was received by Iran's influential former president, Akbar Hashemi Rafsanjani.
The belief that al-Sadr is supported by Iran is shared by many people within and outside of Iraq -- but so far no hard evidence about such support has been made public.
Rubin from the American Enterprise Institute said that, in his personal opinion, Sadr receives more than spiritual support from Iran.
"On 5 April, when the problems broke out with regard to Muqtada al-Sadr and the coalition forces in Iraq, it was Ayatollah al-Haeri who issued threats to the American presence in Iraq. Muqtada al-Sadr doesn't have a lot of grassroots support. He's got some supporters, but I just came back from eight months in Iraq. I watched as Muqtada al-Sadr chartered buses, gave [people] hot meals and such. That takes money, as does Muqtada al-Sadr's radio station and such like this, and they're getting that money through Iran."
The Iranian government has been careful in its comments on the insurgency. While keeping its distance from al-Sadr, Iran expressed strong "regret" [5 April] over the deaths and injuries caused by clashes between al-Sadr's militants and coalition forces.
Some observers point out that Iran has closer ties with one of al-Sadr's rivals, Abdul al-Aziz al-Hakim, a member of the Iraqi Governing Council and head of the Supreme Council for Islamic Revolution in Iraq.
One clear area of mutual benefit is in economic and commercial relations. In recent months, Iraqi dignitaries have made several officials visits to Tehran. Both sides have talked about future plans such as the building of a cross-border oil pipeline.
Nourizadeh said better economic ties are strongly in Iran's interest.
"I think if the Iranians pursue a policy of supporting the new government, if they stop intervening in Iraq's internal affairs, then I'm sure we're going to have very good relations and then Iranians can use their influence in order to bring stability to Iraq and prosperity to Iraq's people and they can participate in rebuilding Iraq," Nourizadeh said.