There are only "some weeks" left to revive the nuclear deal with Iran if it continues its nuclear activities at the current pace, US negotiator Rob Malley said Tuesday.

Malley, in an interview with CNN, warned of a "period of escalating crisis" if diplomacy failed to restore the 2015 nuclear agreement between Iran and world powers known as the Joint Comprehensive Plan of Action (JCPOA).

Negotiations restarted in November, after a five-month hiatus, to try to restore the deal with Iran, which the United States withdrew from under former president Donald Trump in 2018.

The indirect talks have been suspended but Malley said he hoped they would resume "relatively soon."

Iran claims it only wants to develop a civilian nuclear capability but Western powers say its stockpile of enriched uranium goes well beyond that, and could be used to develop a nuclear weapon.

Washington has warned recently that it may soon be too late to revive the JCPOA.

"It really depends on the pace of their nuclear process," said Malley, the US special envoy for Iran. "If they halt the nuclear advances, we have more time.

"If they continue at their current pace, we have some weeks left but not much more than that, at which point the conclusion will be there's no deal to be revived," he said.

"At some point in a not-so-distant future we will have to conclude the JCPOA is no more and we would have to negotiate a wholly different deal and we would go through a period of escalating crisis," he added.

US Secretary of State Antony Blinken said Tuesday that he was not going to set a deadline for the talks.

"I'm not going to put a time limit on it," Blinken told reporters, but the remaining runway for a deal is "getting very, very, very short."

"We continue to have a strong interest in seeing if we can put the nuclear program back into the box that it was in," he said. "But if we can't do that, because Iran will not engage in good faith, then we are actively looking at alternatives and options."

The 2015 agreement ensured sanctions relief for Iran in return for tight curbs on its nuclear program, which was put under extensive UN monitoring.

Trump went on to re-introduce sanctions, prompting Tehran to start disregarding the deal's limits on its nuclear activities in 2019.

Recent rounds of talks have stumbled on which sanctions Washington is prepared to lift, and guarantees demanded by Iran to protect against the prospect of a future US withdrawal.

Iran holds extensive military exercises
Tehran (AFP) Dec 21, 2021 –

Iran fired missiles from land and sea Tuesday as part of five days of military exercises in three provinces, including near its only nuclear power plant, the Revolutionary Guards said.

The military manouevres come after the United States said it was preparing "alternatives" in case negotiations to revive a deal to curb Iran's nuclear programme collapse in Vienna.

"We have carried out exercises to destroy the enemy before they approach the Hormuz islands," Guards navy commander Rear Admiral Alireza Tangsiri said, quoted by the Guards' Sepah News website.

Abu Musa island and the Greater and Lesser Tunb islands, located in the Gulf near the entrance to the Strait of Hormuz, are under Iranian control but are also claimed by the United Arab Emirates.

A fifth of world oil output passes through the Strait of Hormuz.

The military drills dubbed Payambar-e-Azadm, or "Great Prophet", began on Monday in Bushehr, Hormozgan and Khuzestan provinces, each of which touch the Gulf.

They included biological warfare exercises.

The manouevres also saw the deployment of Iranian-made boats that are capable of launching high-precision missiles and reaching speeds up to 75-95 knots.

At dawn on Monday, "in order to increase the defence capability of the armed forces, an exercise was held over the Bushehr nuclear power plant," Mohammad-Taghi Irani, Bushehr's deputy governor for political and security affairs, told Fars news agency.

On December 4, an Iranian air defence test in the Natanz region of central Iran caused an explosion heard about 20 kilometres (12 miles) from the Natanz uranium enrichment facility.