Iran threatened on Monday to restart deactivated centrifuges and sharply step up its enrichment of uranium to 20 percent purity as its next potential big moves away from a 2015 nuclear agreement that Washington abandoned last year.
The threats, made by the spokesman for Iran's nuclear agency, would go far beyond the small steps Iran has taken in the past week to nudge its stocks of fissile material just beyond limits in the nuclear pact.
That could raise serious questions about whether the agreement, intended to block Iran from making a nuclear weapon, is still viable.
Behrouz Kamalvandi, the spokesperson for Iran's Atomic Energy Organisation, confirmed an announcement that Tehran had enriched uranium beyond the 3.67 percent purity that the deal allows, passing 4.5 percent, according to the student's news agency ISNA. That followed an announcement a week ago that it had amassed a greater quantity of low-enriched uranium than permitted.
Iran has said it will take another, third step away from the deal within 60 days but has so far held back from formally announcing what that next step would entail.
Kamalvandi said the authorities were discussing options that included the prospect of enriching uranium to 20 percent purity or beyond, and restarting centrifuges that were dismantled as one of the deal's core aims.
"There is the 20 percent option and there are options even higher than that but each in its own place," Kamalvandi said, according to state television. Restarting IR-2 and IR-2 M centrifuges was an option, he said.
Such threats will 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.
Washington has imposed sanctions that eliminate any of the benefits Iran was meant to receive in return for agreeing to curbs on its nuclear programme under the 2015 deal 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 percent purity would be a dramatic move, since that was the level Iran had achieved before the deal was put in place. It is considered an important intermediate stage on the path to obtaining the 90 percent pure fissile uranium needed to make a bomb.
One of the main achievements of the deal was Iran's agreement to dismantle its advanced IR-2M centrifuges, which are used to purify uranium. Iran had 1,000 of them installed at its large enrichment site at Natanz before the deal was reached. Under the deal, it is allowed to operate only up to two for mechanical 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.
The nuclear diplomacy is only one aspect of a wider confrontation between Washington and Tehran that has threatened to spiral into open conflict since the United States sharply tightened sanctions on Iran from the start of May.
Last month, Trump ordered US air strikes on Iran, only to call them off minutes before impact. Washington's European allies have been warning that a small mistake on either side could lead to war.
The nuclear agreement guaranteed Iran access to world trade in return for accepting curbs on its nuclear programme. Iran says the deal allows it to respond to the US breach by reducing its compliance, and it will do so every 60 days.
"If signatories of the deal, particularly Europeans, fail to fulfil their commitments in a serious way, the third step will be stronger, more decisive and a bit surprising," Foreign Ministry spokesperson Abbas Mousavi said on Monday.
The new US measures in place since May are intended to bar Iran from all oil exports and have succeeded in effectively pushing Iran out of mainstream oil markets.
European countries do not directly support the US sanctions, but have been unable to come up with ways to allow Iran to avert them. Britain, one of Washington's main European allies, was drawn deeper into the confrontation last week when it seized an Iranian tanker it says was bound for Syria, in violation of separate EU sanctions on Syria.
Despite tough talk from Washington and Tehran, there are no signs that either side was prepared for a full-blown conflict.
"As repeatedly announced before, Iran doesn’t seek war against any country but it has well learned how to defend itself,” Major General Abdolrahim Mousavi was quoted as saying by Iranian media.