The International Institute for Strategic Studies (IISS) says Iran has built a network of nonstate alliances across the Middle East over the past 40 years that has allowed it to turn the balance of "effective" power in the region "in its favor."
In a report to be released later on November 7, the London-based think tank says the United States and its regional allies retain superiority in conventional forces over Iran.
However, the sanctions-bound country has managed to counter that superiority by building "networks of influence" with proxies that allow Tehran to have a major influence over the affairs of Syria, Lebanon, Iraq, and Yemen.
Since the 1979 Islamic Revolution, Iran has been recruiting, funding, and arming its network of alliances across the region.
These activities have not stopped since the United States withdrew from a landmark 2015 nuclear deal last year and reinstated sanctions in an attempt to force Iran to negotiate a new agreement, the report said.
In response to the IISS study, titled Iran's Networks Of Influence In The Middle East, a spokesman for the Iranian Embassy in London told the BBC, "If the report means that Iran's role in its region should be respected, it is a welcome sign."
"The policy of ignoring Iran did not work. Iran resisted. Iran has also successfully controlled damages of U.S. economic terrorism," the Iranian Embassy spokesman said.
Iran "is a powerful nation and has a lot of relations with other nations with a lot of initiatives for regional cooperation," he added.
The IISS report says a key ingredient in Iran's struggle for influence has been the Quds Force, the external-operations wing of the Islamic Revolutionary Guards Corps (IRGC).
The report says the force has provided training, funding, and weapons to nonstate actors allied to Tehran and developed unconventional forms of asymmetric warfare, including drone and cyberattacks.
It adds that Lebanon's Shi'ite movement Hizballah "has achieved unique status among Iran's partners" and is "more akin to a trusted junior partner and a brother-in-arms for Iran than a proxy."
Hizballah has played an important role in the conflicts in Syria and Iraq, fighting alongside forces loyal to Syrian President Bashar al-Assad and assisting Iraqi Shi'ite militias, and has become a central interlocutor for Arab militias and political parties with ties to Tehran, it says.
Iran has also supported militant groups in U.S. allies Saudi Arabia, Bahrain, and Kuwait in an effort to "irritate and pressure their governments, and impose a political cost for their partnership with the United States," according to the report.
It noted that the drone and missile strikes on Saudi oil installations in September showed how vulnerable the Arab states in the Persian Gulf are to asymmetric attacks.
In Yemen, Iran's has stepped up support for the Shi'ite Huthi rebels by supplying advanced weaponry to "bog down at a limited cost" its main regional foe Saudi Arabia, which has been leading a military coalition that has been battling the Huthis since 2015.
Tehran also aims to "establish a forward presence" in the strategic Red Sea area of Bab al-Mandab, the report says.