Iran is making steady progress in its nuclear enrichment programme but there is still time to find a diplomatic solution over work the West fears is aimed at making bombs, a former top UN nuclear official said.

Olli Heinonen, who stepped down in August as chief of UN nuclear inspections worldwide, also voiced doubt about reports that Iran's atomic activities were the target of a cyber attack.

Security experts say the release of the Stuxnet computer worm may have been a state-backed attack on the Islamic Republic's nuclear programme, most likely originating in the United States or Israel.

Some analysts believe Iran may be suffering wider sabotage aimed at slowing its nuclear advance, pointing to a series of unexplained technical glitches that have cut the number of working centrifuge machines at the Natanz enrichment plant.

Heinonen said the Stuxnet virus, which Iran said had hit computers used by nuclear staff, had also been discovered in other countries so he found it a 'bit hard to believe' it had been specifically aimed at Iran's Bushehr atomic plant or Natanz.

'This is all speculation until the facts are found,' he told Reuters in a telephone interview on Thursday.

Asked if there had been any indications of past sabotage aimed at Natanz, he said: 'I don't think there is enough technical evidence to say - yes, there has been sabotage (or) no, there has been no sabotage.'

Heinonen noted that Iran's monthly output of low-enriched uranium, which can fuel power plants or provide material for bombs if refined much further, had been stable at about 120 kg.

'Let's assume some machines are failing, the others are then performing better,' the Finnish nuclear expert said.-Reuters