In a recently published report, the International Institute for Strategic Studies states that the global pressure Iran has experienced due to its nuclear development program has taken its toll and slowed down the rate of its weapons development.

"Financial sanctions and oil embargoes imposed since December 2011 by the United States and European Union respectively have tightened the economic pressure on Iran and, along with United Nations Security Council sanctions imposed in June 2010, could yet deal a knock-out blow to the country's development of long-range ballistic missiles," the report claims.

The report goes on to say that although international sanctions did not seem to prevent Iran from developing nuclear materials, "it has stymied efforts to develop and produce the long-range ballistic missiles capable of striking potential targets in western Europe and beyond. If sanctions continue to disrupt Tehran's access to the key propellant ingredients and components needed to produce large solid-propellant rocket motors, Iranian attempts to develop and field long-range ballistic missiles could be significantly impeded, if not halted altogether."

The report details how Iran has for some time planned on targeting Israel using foreign-made missiles: "Wishing to threaten targets as far afield as Israel, Iran began procuring medium-range No-dong missiles, known locally as Shahab-3s, from North Korea in the mid- to late-1990s. The imported No-dong/Shahab-3 missiles, as received and initially tested by Iran in 1998, had a maximum range of only 900km (559 miles), meaning that they could only reach Israel if launched from sites near Iran's border with Iraq."

Iranian engineers reportedly worked for over a decade on developing an improved version of the Shahab-3, which they had called Ghadr-1. The Ghadr-1 has a maximum range of roughly 1,600 kilometers (1,000 miles) — roughly the distance between Israel and Iran (1,700 kilometers, or 1,100 miles).

"Iran does not have the capacity to design, develop and produce new, more powerful ... engines," the IISS report says. "And this is unlikely to change over the next decade. Available evidence also indicates — but does not prove — that Iran cannot reliably build the liquid-propellant engines that power its current inventory of Scud and No-dong/Ghadr-1 missiles, a shortfall that likely leaves the Islamic Republic susceptible to supplier controls and unable to add to its stockpile of operational liquid-fuelled missiles. Iranian engineers may one day establish a capacity to produce near-copies of the Scud and No-dong engines, but such endeavours are rarely successful — replica engines do not perform as well as the originals and often prove to be unreliable."

The IISS focuses on nuclear development and global armament, and claims to be "the world’s leading authority on political-military conflict."