The warning came after CNN, citing unnamed US officials, reported Tuesday that Israel was making preparations to strike Iranian nuclear sites despite the ongoing US-Iran talks.

"We believe that in the event of any attack on the nuclear facilities of the Islamic Republic of Iran by the Zionist regime, the US government will also be involved and bear legal responsibility," Foreign Minister Abbas Araghchi said in a letter to the United Nations published on Thursday.

"Iran strongly warns against any adventurism by the Zionist regime and will respond decisively to any threat or unlawful act by this regime," Araghchi added.

The nuclear talks, which began on April 12, are the highest-level contact between the long-time foes since the United States in 2018 pulled out of a landmark deal between Iran and world powers, during President Donald Trump's first term in office.

Oman, which has mediated the talks, said that a fifth round will take place in Rome on Friday.

The US delegation will include Steve Witkoff, Trump's friend and globe-trotting negotiator, and Michael Anton, the head of policy planning at the State Department who has been involved in technical details, according to a source familiar with arrangements.

A key sticking point in the negotiations has been enrichment. The 2015 deal with Iran, which was negotiated by former president Barack Obama, allowed Iran to enrich uranium at low levels solely for civilian energy.

The Islamic republic currently enriches uranium to 60 percent, far above the 3.67-percent limit set in the 2015 deal but below the 90 percent needed for a nuclear warhead.

- Sanctions over missiles -

Trump, who has vowed to improve on the Obama deal, said last week on a trip to Qatar that he believed Iran had agreed to key conditions and that his diplomacy would avoid military conflict.

US Secretary of State Marco Rubio, testifying Wednesday before Congress, again said that the Trump administration would insist on no enrichment.

"Iran cannot have an enrichment capability, because that ultimately makes them a threshold nuclear power," Rubio said.

Iran is looking for relief from sweeping sanctions imposed in 2018 by Trump, which include penalties on all countries to prevent them from purchasing Iran's key export of petrol.

Rubio, questioned by a lawmaker, suggested that the United States would maintain sanctions over Iran's development of ballistic missiles, a topic that was not addressed explicitly under the 2015 agreement.

"There are sanctions related to terrorism, sanctions related to their ballistic missiles programme, and the like. Those sanctions, if they're not part of the deal, they'll remain in place," he said.

Rubio did not comment on the CNN report, but said it was no secret that Israel has been studying military options.

- 'Devastating response' -

Israel, Iran's sworn enemy, has been threatening to use force against Iranian nuclear sites but has faced resistance from Trump.

On Thursday, Ali Mohammad Naini, the spokesman for Iran's Islamic Revolutionary Guard Corps, warned of a "devastating" response in case of an Israeli attack.

"If the delusional Zionist regime commits a foolish act and launches an attack, it will definitely receive a devastating and decisive response in its small and vulnerable geography," said Naini, according to ISNA news agency.

Also on Thursday, the Iranian army's ground forces unveiled three new drones, adding two reconnaissance and one kamikaze drone to to its arsenal, the official IRNA news agency reported.

Earlier in the day, a group of demonstrators gathered near the Fordow nuclear enrichment plant south of Tehran to voice their support for the country's nuclear activities.

The crowd waved Iranian flags and chanted slogans such as "nuclear energy is our inalienable right" and "no compromise, no surrender, only confrontation with America".

Iran does not recognise Israel and generally refers to it as the "Zionist regime", and the two countries have fought a shadow war for years.

The two foes traded direct attacks last year for the first time, against the backdrop of soaring regional tensions triggered by the Gaza war.