Iran’s quest for nuclear weapons is suffering from production and engineering troubles, Fox News reported on Tuesday.

Two new reports from the Institute for Science and International Security (ISIS) have found that output has slowed dramatically at Iran’s main nuclear facility in Natanz, where centrifuges required to make the enriched uranium needed for nuclear weapons are located.

The reason for the slowdown, according to the reports, is the Stuxnet virus which hit Iran’s computers last year, as well as the United Nations’ sanctions against the Islamic Republic.

David Albright, former United Nations weapons inspector at ISIS, told Fox News, “Iran probably cannot build more than a certain number of these first-generation centrifuges. There’s some parts in them that require high-tech steel and a particular form, and it looks like Iran cannot get any more. The major result is that the output at the Natanz enrichment site is actually decreasing.”

Albright added that the original IR-1 centrifuges are getting old and outdated and Iran needs 1,000 more of them to produce the same amount of low-enriched uranium from a year earlier. He noted that the Stuxnet malware, which targeted the Natanz centrifuges, appears to be causing residual breakage, and the original centrifuges are difficult to manufacture or replace.

The powerful Stuxnet virus targeted Iran’s nuclear facilities and other industrial sites last year. Iran acknowledged that Stuxnet affected a limited number of centrifuges at its main uranium enrichment facility in the central city of Natanz, but claimed its scientists discovered and neutralized the malware before it could cause serious damage.

In April, Iran said its nuclear program had once again been attacked, this time by a different computer virus called Stars.

The Stuxnet attack is widely believed to have been an Israeli cyber-attack, but Israel has not admitted it.