US and Iranian officials said initial indirect talks in Vienna on 6 April aimed at reviving the 2015 Joint Comprehensive Plan of Action (JCPOA), were "constructive", with negotiations set to continue, although direct talks between US and Iranian officials are not taking place. Under the JCPOA between Iran the P5+1 group of countries (the USA, UK, France, Russia, and China plus Germany) Iran agreed to limit its nuclear development in return for the lifting of sanctions.

However, US President Donald Trump’s decision to withdraw from the deal and reimpose sanctions in 2018 prompted Iran to revive its nuclear programme while informing the International Atomic Energy Agency (IAEA) of the steps being taken. The Vienna talks, which involve all the parties to the JCPOA, aim to bring the USA back into the agreement. Iran has insisted that it will not talk directly with the US until sanctions are lifted.

"We do see this as a constructive and certainly welcome step," US State Department spokesman Ned Price told reporters in Washington after the first day of talks. "It is a potentially useful step as we seek to determine what it is that the Iranians are prepared to do to return to compliance with the stringent limitations under the 2015 deal and, as a result, what we might need to do to return to compliance ourselves," he added. Following the closed meetings of the JCPOA signatories Russian envoy Mikhail Ulyanov tweeted that the initial talks were "successful". "The restoration of JCPOA will not happen immediately. It will take some time," he wrote. "The most important thing after today's meeting … is that practical work towards achieving this goal has started." At the meeting, participants agreed to establish two expert-level groups, one to work on the lifting of sanctions and the other to work on nuclear issues.

Iranian television quoted Iran's negotiator, Abbas Araghchi, as also describing the talks as "constructive" but reiterated the demand that the US must lift sanctions before Iran makes any concessions. "Lifting US sanctions is the first and the most necessary action for reviving the deal," he said. "Iran is fully ready to reverse its activities and return to complete implementation of the deal immediately after it is verified sanctions are lifted."

In February, Iran began restricting international inspections of its nuclear facilities in line with a law passed by the Iranian parliament but mediation by International Atomic Energy Agency (IAEA), head Rafael Grossi resulted in some access being permitted for a limited period. Iran will no longer share surveillance footage of its nuclear facilities with the IAEA but it has promised to preserve the tapes for three months. It will then hand them over to the IAEA if it is granted sanctions relief.

Meanwhile, Iran is continuing to ramp up its nuclear activities. On 7 April the spokesman for the Atomic Energy Organisation of Iran (AEOI) Behrouz Kamalvandi said Iran has already produced 55kg of 20% enriched uranium. The law ratified by the Iranian Parliament had specified annual production of 120kg of 20% enriched uranium and measures for implementing that were adopted immediately, he said, adding, “we can reach the specified amount in less than eight months”. The capacity for enriching uranium to 20% has increased compared with the pre-JCPOA era, he added. “Currently we have 16,000 SWUs capacity for enrichment while it was 12,000 SWUs before the nuclear deal was signed.”

Iran is using new generations of centrifuges such as IR-6, increasing output. "Currently, we see the deployment of 2,000 IR2M machines," he said, adding that a cascade of IR-4 centrifuges has been installed and the second cascade will also be put in place. Kamalvandi told ISNA on 5 April that AEOI had also begun testing next-generation IR-9 centrifuges, which are 50 times more powerful than the IR-1.

Under the JCPOA, Iran was allowed to enrich uranium only using IR-1 centrifuges. This is just the latest in a series of measures Iran has taken to reduced its obligations under Articles 26 and 36 of the nuclear deal.