Iran has reportedly placed a sophisticated, Russian-made air defence system around an underground uranium enrichment facility at Fordow.

The S-300, capable of intercepting airborne targets up to 150 miles away, has traditionally been seen as a significant obstacle facing any country attempting an air strike on Iran’s nuclear installations.

In 2010, Russia agreed to suspend the supply of the system as part of the international pressure on Iran to limit its nuclear development, but in April 2015 the Kremlin announced that it was scrapping the restriction.

Iranian state TV this week released footage of the defence system arriving at the nuclear plant.

Although Israeli defence officials would not comment on the report, the US State Department out out a statement saying that it was “concerned about the provision of sale to Iran of sophisticated defence capabilities such as this S-300… we have long objected to the sale [to] Iran of these kinds of capabilities.”

Israel’s Prime Minister’s Office and the Foreign Ministry also refused to comment on Iranian President Hassan Rouhani’s announcement that construction would begin on two new nuclear power plants, both to be built by Russia.

However, analysts say that privately, Israeli officials fear these developments are another sign that Iran is using the time secured by the 2015 nuclear deal to build up its defences against any military attempt to end its nuclear programme.

“This is part of what the pessimists had been anticipating which is basically we have a period of Iran not enriching uranium, which is the main component of building nuclear weapons, but they were planning to improve in every other field that allows them to improve their technology, conduct research and work on strategy,” said Eldad Pardo, an Iran expert at the Hebrew University.