The announcement on Saturday that Iran had satisfied its obligations under a nuclear deal with world powers was expected to pave the way for a new economic reality in the Islamic Republic, free from years of harsh international economic sanctions.

The formal declaration in Vienna marked the official start of the landmark July deal between Tehran and six world powers — the U.S., Britain, France, Russia, China and Germany. In advance of that announcement, Iran and the U.S. conducted a prisoner swap that saw seven Iranians held in America released in exchange for four Iranian prisoners with dual nationalities — including Washington Post bureau chief Jason Rezaian.

"All sides remain firmly convinced that this historic deal is both strong and fair," said European Union foreign policy chief Federica Mogherini, speaking alongside Iranian Foreign Minister Mohammad Javad Zarif. "This is an encouraging and strong message that the international community must keep in mind in our efforts to make the world a safer place."

U.S. Secretary of State John Kerry, speaking separately, said Iran "has kept its word and we shall do the same." However Kerry emphasized the need for the UN and world powers to remain vigilant in ensuring Iranian compliance going forward.

As the speeches in Vienna were still taking place, Iran's moderate President Hassan Rouhani, a strong supporter of the deal, tweeted in celebration: "#ImplementationDay--I thank God for this blessing & bow to the greatness of the patient nation of Iran. Congrats on this glorious victory!"

While some financial issues may take days to figure out, Iran greeted the news with muted celebrations since the Vienna statement didn't come until well after midnight in Tehran. However celebratory messages circulated on social media.

"Hello to life without sanctions," said one message shared on the Telegram app and other social messaging apps. Another read: "Thank you Rouhani, Thank you Zarif."

For Iran, long out in the economic cold over its contested atomic program, implementing the nuclear deal will be a welcome thaw.

More than $30 billion in assets overseas will become immediately available to the Islamic Republic. Iran's Central Bank Governor, Valiollah Seif, was quoted by the official IRNA news agency as saying that Iran will not transfer the cash and instead will use it to import the goods it needs. Official Iranian reports have set the total amount of frozen Iranian assets overseas at $100 billion.

A European oil embargo on Iran will end. Already, some 38 million barrels of oil are in Iran's floating reserves, ready to enter the market, according to the International Energy Agency.

All that means even more money coming into the country, allowing it to undertake needed repairs to its oil and gas fields to boost its own production. Iran is home to the world's fourth-largest proven reserve of crude oil and ranks second in proven natural gas reserves behind Russia.

Tehran already seems to be making plans for its post-sanctions economy and infrastructure. Transport Minister Abbas Akhondi told the official IRNA news agency Saturday that his government had agreed to buy 114 new planes from the European consortium Airbus. Iran is looking to buy up to 400 new planes to replace its aging commercial fleet — some of which has been grounded due to a lack of spare parts.

Sizeable financial challenges will remain for Iran, a country in which ATMs don't link to the global banking system and restaurants can't accept foreign credit cards. Local banks remain lumbered with bad debt, inflation is still high and unemployment stands around 10 percent.

The International Monetary Fund in October noted that some businesses and consumers were putting off major purchases in hopes of getting higher-quality foreign goods when sanctions end. This delayed spending is dragging down domestic growth, but could amplify the economic boost delivered by the sanctions lifting.

Meanwhile, the global economy is still staggering after the Great Recession and oil is selling at around $30 a barrel, a 12-year low already affecting Iran's oil-producing neighbors in the Gulf. Any new Iranian supply to the market is likely to keep oil prices down.

"In terms of the global backdrop, Iran's reintegration could hardly come at a worse time," an October report by the Dubai-based bank Emirates NBD said. "Ultimately, we still suspect that growth can rebound sharply."

Under the deal, the United Nations' arms embargo on the country continues, as do ballistic missile restrictions.

Since July, there has been some hard-line pushback. Iran's powerful Revolutionary Guard has launched missiles and shown footage of an underground weapons base in the Islamic Republic, and Supreme Leader Ayatollah Ali Khamenei has warned against Western influence spreading in the country.

But this week, when U.S. sailors were captured by Iran after straying into its territory, the Islamic Republic let them leave within a day after direct contacts between Kerry and Zarif. The two diplomats formed close ties during the nuclear negotiations.

Kerry said Saturday that the mutual prisoner swap was not formally linked to the nuclear deal, but that it was "accelerated in light of the relationships forged ... in the nuclear talks."

The deal also could affect Iran's upcoming parliamentary election in February, further changing the balance of political power in the Islamic Republic. Already, analysts have said they believe it will boost allies of moderate President Hassan Rouhani, whose administration helmed the deal.

But since the deal, there have been a series of legal cases in Iran targeting poets, filmmakers, artists, activists and journalists, which analysts attribute to hard-liners' continuing struggle with moderates.

Prominent analyst Sadeq Zibakalam said implementation of the nuclear deal has brought a genuine rapprochement between Iran and the West for the first time in nearly four decades.

"It's the first time, 37 years after Iran's 1979 revolution, that Iran has succeeded in détente with the West, specifically with the U.S. despite radical and hard-line opponents both inside Iran and America as well as the Israeli lobby and Saudi opposition," Zibakalam said.

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Gambrell reported from Dubai, United Arab Emirates. Follow him on Twitter at www.twitter.com/jongambrellap .