Financial sanctions and oil embargoes imposed since December 2011 by the United States and European Union respectively have tightened the economic pressure on Iran, according to an important report here Monday.

Along with United Nations Security Council sanctions imposed in June 2010, these measures could yet deal a knock-out blow to the country's development of long-range ballistic missiles, the International Institute for Strategic Studies (IISS) said in a comprehensive dossier.

"There is mounting evidence to suggest that, whereas the sanctions regime has not prevented Tehran from operating an increased number of centrifuges for uranium-enrichment activities or adding to its stockpile of fissile material, it has stymied efforts to develop and produce the long-range ballistic missiles capable of striking potential targets in western Europe and beyond", the respected defence think tank said.

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, IISS underlined.

Soon after the start of the Iran-Iraq War in 1980, Tehran initiated a two-track effort to acquire ballistic missiles and related technologies to compensate for its barely operational air force, the study pointed out.

The first track focused on the immediate acquisition of short-range, liquid-propellant Scud-B missiles from Libya, Syria and North Korea for use against Iraqi cities during the latter stages of the war. The perceived success of the missile attacks led Iran to purchase additional 300km-range Scud-Bs from Pyongyang, along with 500km-range Scud-Cs, in the 1990s, which it renamed Shahab-1 and -2.

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 institute added. The imported No-dong/Shahab-3 missiles, as received and initially tested by Iran in 1998, had a maximum range of only 900km, meaning that they could only reach Israel if launched from sites near Iran's border with Iraq.

In a quest to enhance pre-launch survivability, Iranian engineers spent almost a decade modifying the Shahab-3 to create a longer-range version of the missile, dubbed Ghadr-1.

The Ghadr-1 has a maximum range of roughly 1,600km when carrying a relatively light payload of 750kg and is believed to have entered military service some time after 2007, the research institute added. If fitted with a heavy payload, such as a notional first-generation nuclear warhead weighing upwards of 1,300kg, the Ghadr-1's maximum range would be reduced to roughly 1,100km.

Iran does not have the capacity to design, develop and produce new, more powerful liquid-fuelled engines, and this is unlikely to change over the next decade, it noted.

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 report suggested.