A deal with world powers ended a "manufactured crisis" over Iran's nuclear programme, its foreign minister said Wednesday as he arrived home from negotiating the agreement which angered US lawmakers.

As attention turned to the lengthy process of implementing the complex accord, Mohammad Javad Zarif said the world had no cause to fear Iran's nuclear activities.

Zarif, who led Iran's negotiating team in the 18 straight days of "tough" talks that culminated in Tuesday's historic agreement, said common ground had been found.

"We will take measures and they will do their part," he told reporters at Tehran's Mehrabad airport, referring to the six powers led by the United States with whom Iran is now bonded in the nuclear pact.

"It will happen in around four months from now," he said of the formal implementation of the deal.

Zarif's comments came after after a night of celebrations in Tehran where his own name was chanted in the streets by joyous Iranians.

Many festooned their cars with balloons and danced on the street to celebrate the prospect of an end to the long years of economic hardship caused by Western sanctions.

"Maybe the economy is going to change, especially for the young people. I was thinking about leaving, but now I will stay to see what happens," said Giti, 42, a computer programmer.

But only hours earlier in Washington the deal came under intense scrutiny.

The speaker of the Republican-led US House of Representatives, John Boehner, said the agreement was "likely to fuel a nuclear arms race around the world".

Zarif hit back at the deal's biggest critic, Israeli Prime Minister Benjamin Netanyahu, head of the region's sole if undeclared nuclear state, who branded the agreement a "historic mistake".

"Netanyahu kicked up a fuss as he is upset that Iran managed to get sanctions lifted and prevent a manufactured crisis," Zarif said.

- Obama faces hard sell -

Iran has always denied seeking an atomic bomb and that stance was reiterated by President Hassan Rouhani after Tuesday's agreement.

Soon after the deal was announced the White House launched a campaign to stop sceptics at home and abroad from derailing the hard-won accord.

US President Barack Obama was to hold a press conference later on Wednesday to try to convince Americans of the benefits of the deal, which is likely to face a bruising passage through Congress.

US lawmakers have 60 days to review the accord but Obama has vowed to use his presidential veto over any attempt to block it.

In return for curbs on its atomic programme for at least 10 years, Iran will be freed from sanctions that have crippled its economy.

Tehran has also agreed to allow the UN nuclear watchdog tightly controlled access to its military bases, an Iranian official said.

And it will slash by around two-thirds the number of centrifuges -- which can make fuel for nuclear power stations but also the core of a nuclear bomb -- from around 19,000 to just over 6,000.

Obama said the accord meant "every pathway to a nuclear weapon is cut off".

"This deal offers an opportunity to move in a new direction. We should seize it," he said, pointing to a broader effort to end the hostility between the two governments that has persisted ever since the overthrow of the US-backed shah in the Islamic revolution of 1979.

- Cooperation against IS -

Washington hopes the accord may lead to more cooperation with Iran at an explosive time in the Middle East after the Islamic State militant group surged last year, seizing vast swathes of Syria and Iraq.

Russian Foreign Minister Sergei Lavrov said the deal paves the way for a "broad" coalition to fight the Sunni extremist group which is as hostile to Shiite Iran as it is to the West.

"It removes the barriers -- largely artificial -- on the way to a broad coalition to fight the Islamic State and other terrorist groups," Lavrov said.

EU foreign policy chief Federica Mogherini told Sky Italia the deal "opens the way for a new confidence" in combating IS.

But it has alarmed some of America's most important Middle East allies, including Sunni regional power Saudi Arabia.

French Foreign Minister Laurent Fabius said he had accepted an invitation to visit Tehran soon.

With Iran set to reopen for business with the progressive lifting of UN and Western sanctions, he was likely to be the first in a long line of top diplomats beating a path to Tehran.

France was with Britain, China, Germany, Russia and the United States one of the six powers that reached the deal with Iran.

But Fabius denied commercial considerations had played any part, saying that while "trade is very important," France backed a deal with Iran "for strategic reasons because we wanted to avoid nuclear proliferation."

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