The UN nuclear watchdog on Saturday said Iran had put in place all nuclear measures required under a deal reached with six world powers in July, paving the way for crippling sanctions on the Islamic Republic to be lifted within hours or days.
"Iran has carried out all measures required under the (July deal) to enable Implementation Day (of the deal) to occur," the Vienna-based International Atomic Energy Agency (IAEA) said in a statement.
The announcement marks the consummation of the July 14, 2015 nuclear agreement. Under the deal, Iran agreed to shrink its atomic programme in exchange for the lifting of some EU, US and UN sanctions, which would allow billions of dollars of investment to flow into the country.
The EU procedure for lifting sanctions should be rapid. An official decision of the European Council, which brings together leaders of 28 EU members, is required to finalise the process, together with a publication in the EU's Official Journal.
Iran's expected return to an already glutted oil market is one of the factors contributing to a global rout in oil prices, which fell below $30 a barrel this week for the first time in 12 years. Tehran says it could boost exports by 500,000 barrels per day within weeks.
The IAEA is in charge of verifying that Iran has carried out all of the nuclear-related steps required in the deal it struck with the United States, Russia, China, Britain, France and Germany.
Since July, Iran has drastically reduced the number of centrifuges installed at its enrichment sites, shipped tonnes of low-enriched uranium materials to Russia and dismantled the core of its Arak nuclear reactor.
Iran has always denied wanting nuclear weapons, saying its activities are exclusively for peaceful purposes such as power generation.
The Vienna agreement was sealed after two years of rollercoaster negotiations following the June 2013 election of Iranian President Hassan Rouhani.
The highly complex deal drew a line under a standoff dating back to 2002 marked by failed diplomatic initiatives, ever-tighter sanctions, defiant nuclear expansion by Iran and threats of military action.
In addition it put Iran and the United States on the road to better relations some 35 years after the Islamic revolution that toppled the US-backed shah, and at a particularly explosive time in the Middle East.
The deal has more than a decade to run, which is likely to be a bumpy road, experts say, not least if more hardline governments take power in Tehran or Washington.
The two countries are still far from being best friends, as witnessed by Iran's recent capture of 10 US sailors in Iranian waters, although their improved relations did help ensure their swift release.
Iran violated a UN resolution in October when it test-launched a medium-range missile capable of carrying a nuclear warhead, a UN panel of experts concluded in a report in December.
A "snapback" mechanism ensures that many of the sanctions can be swiftly reimposed, and a special joint commission is meant to handle any misunderstandings.
The implementation of the nuclear deal comes after the Iranian government released four US dual national prisoners including Jason Rezaian, the Washington Post’s Tehran correspondent who was charged with espionage, as part of a prisoner swap deal with the United States.
According to Iranian sources, the released Americans also include Saeed Abedini, a pastor from Idaho, Amir Hekmati, a former Marine from Michigan, and Iranian-American businessman Siamak Namazi.
The Tehran prosecutor's office said the inmates were freed "within the framework of exchanging prisoners," as Iranian state run news agency IRNA reported that the United States had also freed seven Iranians.
IRNA named the seven Iranians as Nader Modanlo, Bahram Mechanic, Khosrow Afghahi, Arash Ghahreman, Tooraj Faridi, Nima Golestaneh and Ali Sabouni.
A US official confirmed on Saturday that the US granted clemency to seven Iranians and dropped charges against 14 more in exchange for the release of four Americans held in Iran, a US official said Saturday.
A US official said Iran has also released a fifth American, identified as Matthew Trevithick in a move unrelated to the prisoner swap process, and promised to help the US find out whereabouts of the former FBI agent Robert Levinson who went missing in Iran almost nine years ago.