By David Brennan, Newsweek: A new report has warned that Iran is leveraging its asymmetric warfare networks to establish a military advantage over the U.S. and its allies in the Middle East, as Washington and Tehran maintain a tense standoff over Iran's nuclear research program.

The International Institute for Strategic Studies (IISS) published a new report on Thursday -- titled Iran's Networks of Influence in the Middle East — detailing Tehran's success in establishing a series of non-state forces across the region to protect and further its interests.

While the U.S. and its allies are operating with conventional military forces, the report said Iran's strength lies in its influence within non-state militias and insurgent groups in several nations.

IISS said this "third-part capability" has become more significant than Tehran's ballistic missile program, its nascent nuclear capabilities or its large -- though outdated -- conventional armed forces.

Though the conventional balance is still in favor of the U.S. -- by far the most advanced and well-funded military in the world -- Iran's capability in the so-called "gray zone" has shifted the balance of effective force towards Tehran.

IISS said Iranian investment in its asymmetric network "has consistently delivered Iran advantage without the cost or risk of direct confrontation with adversaries." It allows the nation to launch attacks on enemies with some level of deniability.

The network comprises some 200,000 fighters, IISS estimated, all of which are underpinned by the operations of the Quds Force -- a secretive arm of the Islamic Revolutionary Guard Corps tasked with foreign operations and led by Major General Qasem Soleimani.

The Lebanese Hezbollah militia can attack Israel, Houthi rebels in Yemen can attack Saudi Arabia, and Shi'ite militias in Iraq can attack Americans. The strategy has "consistently delivered Iran advantage without the cost or risk of direct confrontation with adversaries," IISS said.

"Iran avoids symmetrical state-on-state conflict, knowing it will be outgunned. Instead, it pursues asymmetrical warfare through non-state partners," the report added. Rather than taking on fellow states, Iran is "fighting and winning wars 'fought amongst the people.'"

Tehran's strategy is thriving in the modern Middle East, where IISS noted conflicts are now "complex and congested battle spaces involving no rule of law or accountability, low visibility and multiple players who represent a mosaic of local and regional interests".

Iran has been "opportunistic" and flexible in adapting to local demands, IISS said. In Iraq, Tehran focused on arming and training Iraqi militias fighting the U.S. occupation. But in Syria, Iran has worked to bolster President Bashar al-Assad's established government against Western-backed rebel fighters.

And in Lebanon, Iran's support of Hezbollah has helped turn a militia into a parallel military and political force that overshadows the national army and wields huge influence within government.

This has all come at a cost. IISS estimates that Iran's activities in Syria, Iraq and Yemen have cost the economy some $16 billion.

Meanwhile, Hezbollah is receiving around $700 million in support each year and Israeli military officials say Iran is funneling another $100 million to Hamas and Palestinian Islamic Jihad in the Gaza Strip annually.

Iran's regional influence has been a constant chagrin for the U.S. and its allies. But recent anti-government unrest in Iraq and Lebanon has threatened Tehran's reach. The regime is so concerned that Soleimani reportedly personally intervenedin Iraq to forestall an imminent coup against the beleaguered administration there.

But IISS noted that Iran's influence mainly comes through non-state actors, meaning its regional power is less threatened by the fall of specific regimes.

This does, however, limit Tehran's options. "Its influence relies on groups that either do not want to directly rule (as in Hezbollah in Lebanon) or are not capable of and equipped for governance (as in Iraq)," the report explained.

First published in Newsweek.

David Brennan is currently a Senior Reporter for Newsweek covering world politics and current affairs. Prior to joining Newsweek in early 2018, he reported on British politics and global current affairs as a staff writer at International Business Times. He has also held reporting roles at a selection of trade publications covering the healthcare, transport and property industries.