Iran has been hit by a second computer virus, a senior military official has said.

He suggested it was part of a concerted campaign to undermine the country's disputed nuclear programme.

Gholam Reza Jalali, the head of an Iranian military unit in charge of combating sabotage, said that experts discovered the "espionage virus," which he called "Stars."

"The Stars virus has been presented to the laboratory but is still being investigated," Jalali said in a report posted on his organisation's website, paydarymelli.ir. "No definite and final conclusions have been reached."

He did not say what equipment or facilities the virus targeted, or when experts first detected it.

"Stars" is the second serious computer worm to hit Iran in the past eight months. Late last year, a powerful virus known as Stuxnet targeted the country's nuclear facilities and other industrial sites.

Iran has acknowledged that Stuxnet affected a limited number of centrifuges - a key component in the production of nuclear fuel - at its main uranium enrichment facility in the central city of Natanz. But Tehran has said its scientists discovered and neutralised the malware before it could cause serious damage.

Jalali downplayed the impact of Stars, but said it is "harmonious" with computer systems and "inflicts minor damage in the initial stage and might be mistaken for executive files of governmental organisations."

Jalali heads a military unit called Passive Defence that primarily deals with countering sabotage. The unit was set up on the orders of Iran's Supreme Leader Ayatollah Ali Khamenei.

A separate unit has also been set up by Iran's Ministry of Information Technology and Telecommunications to decode incoming computer viruses and neutralise them, Jalali said.

Iran blames the United States and Israel for the Stuxnet attack.