The International Crisis Group (ICG) said on Monday that Iran has exercised its influence on Iraq with considerable restraint since the 2003 US-led invasion, although it has had the capacity to do otherwise.
Tehran's priority is to prevent Iraq from re-emerging as a threat - military, political or ideological - said the Brussels-based organisation.
"It is thus intent on preserving Iraq's territorial integrity, avoiding all-out instability, encouraging a Shia-dominated, friendly government, and keeping the US preoccupied," said the report.
Tehran has been accused by Washington of nefarious interference in its neighbour, by Arab leaders of seeking to establish an Islamic republic in Iraq, and by prominent Iraqi officials of manipulating elections, supporting anti-US violence, and infiltrating the country.
The notion is widely accepted in Iraq, the Arab world and the US that Iran is intent on destabilising Iraq, moulding its politics decisively, and establishing a like-minded, compliant government.
Shia leader Muqtada al-Sadr's uprising in April 2004 heightened fears that Iran might be backing anti-US violence.
Iran also has been accused of facilitating the movement of anti-US groups such as Ansar al-Islam, and of being responsible for the assassination of Iraqi security officials.
More recently, the January triumph in elections for Iraq's national assembly of the Shia-based United Iraqi Alliance appeared to vindicate those who suspect an Iranian effort to install a loyal, theocratic government.
"There is no indication that Iranian electoral manipulation is anything more than speculation or that the Shia's victory was anything other than the political translation of their demographic predominance"
International Crisis Group
But the ICG report said: "In fact, there is no indication that Iranian electoral manipulation is anything more than speculation or that the Shia's victory was anything other than the political translation of their demographic predominance.
"Nor has any concrete evidence been presented to bolster the claim that Iran is either actively promoting the insurgency or seeking to maximise instability."
However, the ICG said Iranian security agencies are active in southern Iraq, Baghdad and Kurdistan, and that Tehran has tried to influence Iraq's political process by giving support to prominent political parties.
"Even then, and while the record of the past two years suggests a solid Iranian motive to interfere in Iraq and plenty of Iranian activity, it also suggests little resonance, and, therefore, a negligible impact, on Iraqi society.
"This is because of a deep suspicion and resentment on the part of many Iraqis toward their neighbour," said the ICG.
But the organisation warned the continuation of Iran's relatively cautious attitude depends on relations with Washington.
"While the record of the past two years suggests a solid Iranian motive to interfere in Iraq and plenty of Iranian activity, it also suggests little resonance, and, therefore, a negligible impact, on Iraqi society"
So long as these remain turbulent, Iran is likely to view events in Iraq as part of its broader rivalry with the US.
"The best approach would combine greater US carrots - for example security guarantees and a relaxation of US sanctions - with EU sticks, including the already announced support for UN Security Council action in the event Iran does not verifiably renounce any military nuclear effort," said Joost Hiltermann, the ICG's Middle East project director.
The Brussels-based International Crisis Group is a non-profit, multinational organisation working through field research and analysis as well as high-level advocacy to seek to prevent and resolve deadly conflict.
It produces regular analytical reports and updates on the state of conflicts or potential conflicts around the world.