GENEVA/DUBAI (Reuters) - Iran threatened on Monday to restart deactivated centrifuges and ramp up enrichment of uranium to 20% purity in a move away from the 2015 nuclear deal, but the head of Iran’s Revolutionary Guards insisted the world knows Tehran is not pursuing nuclear arms.

The threats to ramp up enrichment, made by Tehran’s nuclear agency spokesman, would go far beyond the small steps Iran has taken in the past week to nudge stocks of fissile material just beyond limits in the pact that Washington abandoned last year.

They would reverse the major achievements of the agreement, intended to block Iran from making a nuclear weapon, and raise serious questions about whether the accord is still viable.

Iran omitted important details about how far it might go to returning to the status quo before the pact, when Western experts believed it could build a bomb within months.

But Major General Hossein Salami, the head of the Revolutionary Guards, denied Iran was pursuing a nuclear weapon.

“Why do they globally sanction us about the nuclear issue when the world knows that we are not pursuing a weapon? In reality they are sanctioning us because of knowledge,” Salami was quoted as saying by the semi-official Tasnim news agency.

“Nuclear weapons have no place in Islam. Islam never approves of weapons of mass destruction,” he added.

Despite the Iranian threat to boost enrichment, the United States said its renewed sanctions against Tehran were working and warned Iranian leaders not to underestimate U.S. resolve.

“President Trump’s maximum pressure campaign against Iran is working,” White House national security adviser John Bolton told a pro-Israel group in Washington. “We’re just getting started. ... The president’s goal is to get a new deal that would be negotiated in the best interests of the United States.”

U.S. Vice President Mike Pence, who spoke to the same group, added a warning: “Iran should not confuse American restraint with a lack of American resolve,” reiterating Washington’s resolve to protect U.S. personnel and citizens in the Middle East.

Nuclear diplomacy is one aspect of a wider confrontation between Washington and Tehran that has threatened to spiral into open conflict since the United States tightened sanctions from May.

Behrouz Kamalvandi, spokesman for Iran’s Atomic Energy Organisation (IAEA), confirmed that Tehran had enriched uranium beyond the 2015 deal’s limit of 3.67% purity, passing 4.5%, according to news agency ISNA.

The IAEA - the U.N. nuclear watchdog - confirmed it had verified Iran’s enrichment was beyond 3.67%.

Iran has said it will take another, third step away from the deal within 60 days. Kamalvandi said options included enriching uranium to 20% purity or beyond, and restarting IR-2 M centrifuges dismantled under the deal.

Such threats put new pressure on European countries, which insist Iran must continue to comply with the agreement even though the United States is no longer doing so.

French President Emmanuel Macron was sending his top diplomatic advisor to Iran on Tuesday and Wednesday to try to help defuse tensions, a presidential official said. The White House said Trump had spoken to Macron on Monday to discuss efforts to ensure Iran does not obtain a nuclear weapon.

The Iran Nuclear Deal: tmsnrt.rs/2YyMyq0

FILE PHOTO: The Iranian flag flutters in front the International Atomic Energy Agency (IAEA) headquarters in Vienna, Austria March 4, 2019. REUTERS/Leonhard Foeger/File Photo

CENTRIFUGES

The sanctions imposed by Washington threaten to eliminate the benefits Iran was meant to receive for agreeing to curbs on its nuclear program with world powers. The confrontation has brought the United States and Iran close to the brink of conflict, with President Donald Trump calling off air strikes last month minutes before impact.

Enriching uranium up to 20% purity would be a dramatic move, since that was the level Iran achieved before the deal, although back then it had a far larger stockpile than it is likely to be able to rebuild in the short term.

It is considered an important intermediate stage on the path to obtaining the 90% pure fissile uranium needed for a bomb.

One of the main achievements of the deal was Iran’s agreement to dismantle its advanced IR-2M centrifuges, used to purify uranium. Iran had 1,000 of them installed at its large Natanz enrichment site before the deal. Under the deal, it is allowed to operate only up to two for testing.

Still, the threatened measures also appear intended to be sufficiently ambiguous to hold back from fully repudiating the deal. Kamalvandi did not specify how much uranium Iran might purify to the higher level, nor how many centrifuges it would consider restarting. He did not mention other more advanced centrifuges, including the most advanced, the IR-8. Iran has said all the steps it is contemplating are reversible.

‘PIRACY, PURE AND SIMPLE’

European countries do not directly support the U.S. sanctions, but have been unable to come up with ways to allow Iran to avert them.

In a separate standoff, Iran’s foreign minister accused Britain of “piracy” for seizing an Iranian oil tanker last week. Britain says the ship, which was boarded by Royal Marines as it was entering the Mediterranean off Gibraltar, was bound for Syria in violation of European Union sanctions over the conflict there.

“Iran is neither a member of the EU nor subject to any European oil embargo. Last I checked, EU was against extraterritoriality. UK’s unlawful seizure of a tanker with Iranian oil on behalf of #B_Team is piracy, pure and simple,” Iran’s Foreign Minister Mohammad Javad Zarif tweeted on Monday, using ‘B team’ as a derisory term for the Trump administration.

Iran says the deal allows it to respond to the U.S. breach by reducing its compliance, and it will do so every 60 days.

Zarif also tweeted that world powers will not be able to negotiate a better deal than the 2015 nuclear deal.

“#B_Team sold @realDonaldTrump on the folly that killing #JCPOA thru #EconomicTerrorism can get him a better deal,” Zarif wrote, referring to the deal by its acronym for the Joint Comprehensive Plan of Action.

“As it becomes increasingly clear that there won’t be a better deal, they’re bizarrely urging Iran’s full compliance. There’s a way out, but not with #B_Team in charge.”