Iran now has an effective military advantage over the U.S. and its allies in the Middle East because of its ability to wage war using third parties such as Shia militias and insurgents, The Guardian reports citing a military thinktank.

In one of the most detailed assessments of Iran’s strategy and doctrine across Lebanon, Syria, Iraq and Yemen, the International Institute for Strategic Studies (IISS) concludes Iran’s “third party capability” has become Tehran’s weapon of choice.

The 16-month IISS study called Iran’s Networks of Influence claims these networks are more important to Iranian power than either its ballistic missile program, putative nuclear plans or its conventional military forces.

Overall, conventional military balance is still in favour of the U.S. and its allies in the region, the report concludes, but the balance of effective force is now in Iran’s favour.

Despite U.S. sanctions, the report says, Iran has met little international resistance for its strategy, even if it is now facing a fresh challenge from anti-Iranian nationalist protesters within some of the countries in which it wields influence. The findings are likely to strengthen the position of Western diplomats who argue that any new nuclear deal with Iran will have to include not only updated constraints on the country’s nuclear program, but also commitments on its regional behaviour.

The network, operating differently in most countries, has been designed, resourced and deployed by Tehran as its principal means of countering regional adversaries and international pressure, the IISS says. The policy “has consistently delivered Iran advantage without the cost or risk of direct confrontation with adversaries”.

The report finds “Iran is fighting and winning wars ‘fought amongst the people’, not wars between states. Iran avoids symmetrical state-on-state conflict, knowing it will be outgunned. Instead, it pursues asymmetrical warfare through non-state partners.”