Iran's Revolutionary Guards claimed on Sunday that an Israeli stealth drone had been brought down above the Natanz uranium enrichment site in the centre of the country.

The semi-official Fars news agency reported that Iran's elite forces had intercepted and brought down an unmanned aircraft belonging to "the Zionist regime". The news was announced in a statement published by the guards, but it was not clear when the incident, if true, happened.

"This mischievous act once again reveals the adventurist nature of the Zionist regime [of Israel] and added another black page to this fake and warmongering regime's file which is full of crimes," said the Revolutionary Guards' statement.

The state news agency ISNA reported that the aircraft was "of the stealth, radar-evasive type and it intended to penetrate the off-limits nuclear area in Natanz … but was targeted by a ground-to-air missile before it managed to enter the area."

A spokesman for the Revolutionary Guards later told Iranian television that parts of the aircraft had been retrieved. Iran claimed to have reverse engineered a drone after capturing an American RQ-170 Sentinel in 2011.

"Major parts of the devices of the drone are intact and have been received by our friends that can be used for further information," said General Ramazan Sharif. He did not say when the aircraft was shot down, but said it was "identified upon arrival in Iranian airspace". He said authorities allowed it to fly for a short time to determine its destination.

Israeli political and military officials said they never respond to such claims. They have repeatedly threatened to take military action against Iran's nuclear installations, but have been reluctant to do so without US backing or participation.

Natanz is Iran's main uranium enrichment site, housing more than 16,000 centrifuges. About 3,000 more are at the Fordo plant, buried inside a mountain and hard to destroy.

Israel says Iran is developing nuclear weapons at the sites which it intends to use in attacks on the Jewish state. The Israeli prime minister, Binyamin Netanyahu, has repeatedly said the Iranian nuclear programme is an existential threat to his country. Iran insists it is enriching uranium is for civilian purposes.

Iran and the P5+1 powers – Britain, China, France, Russia, the United States and Germany – reached a six-month interim agreement under which Iran suspended part of its nuclear activities in return for a partial lifting of international sanctions.

In July, that deal was extended by four months until November to give the two sides more time to negotiate a final accord aimed at ending 10 years of tensions over Iran's nuclear programme. The sides remain split on how much uranium enrichment Iran should be allowed to carry out.

Washington wants Tehran to slash its programme by three-quarters, but Iran wants to expand enrichment tenfold by 2021, chiefly to produce fuel for its Bushehr nuclear power plant.

Israel opposes any agreement allowing Tehran to keep part of its uranium enrichment programme.