Oil revenues to be paid to Tehran in first phase of nuclear agreement, with warmer relations expected across region

The west is likely to start easing crippling sanctions on Iran in the new year, following the breakthrough agreement in Geneva to freeze and reverse Iran's nuclear programme.

"The focus for the coming weeks has to be swift implementation," said a senior western diplomat.

The accord reached in Geneva on Sunday morning represents a first, six-month phase of a process in which Iran will accept limits on its nuclear programme in return for sanctions relief.

According to US calculations, the interim deal will be worth up to $7bn (£4.3bn) to Iran, made up of $4.2bn in Iranian oil sales revenue unblocked from frozen accounts; $1bn repatriated from petrochemical sales; a possible $500m in extra production and sales by the Iranian car industry due to the lifting of the ban on imports of car parts; and the unblocking of $400m in Iranian frozen assets to help pay the costs of Iranian students abroad. A suspension on a ban on Iran's trade in gold and other precious metals is expected to bring in smaller amounts.

France's foreign minister, Laurent Fabius, said EU ministers would discuss the lifting of partial sanctions as early as December and that a "Europe-wide" decision was necessary for easing some of the punitive measures that the EU has imposed on Tehran. "[That meeting] is expected in several weeks, for a partial lifting that is limited, targeted and reversible," he told radio station Europe 1.

The Geneva deal, struck between Iran and a six-nation group comprising the US, three European states, Russia and China, mediated by the EU's foreign policy chief, Lady Ashton, is expected to trigger a flurry of diplomacy. This will include an EU initiative to try to reassure Iran's regional rivals, enemies and sceptics, such as Israel and Saudi Arabia, of the value of an agreement that, for the first time in a decade, has Tehran agreeing to roll back its nuclear projects under intrusive daily inspection by United Nations monitors.

European and International Atomic Energy Agency (IAEA) experts are to confer this week on how to verify the implementation of the accord in Iran, which will rely heavily on IAEA expertise and manpower to inspect Iran's nuclear-related sites.

Diplomatic efforts will also be made to bolster Iranian reformists under President Hassan Rouhani to try to reinforce his flanks against a conservative backlash in Iran.

"The [Iranian] government can show they are really delivering on their promise to improve relations with the west," said a senior diplomat. "I hope it will change Iran's relations, particularly with the west, for the better. This will hopefully recreate more confidence and trust. I know that for countries in the region there are other issues that are very important – that is Iran's regional role."

Ashton and the six-nation group will soon start work preparing further negotiations with the Iranians with a view to sealing a final settlement within six months. The task could be far more challenging than clinching the interim accord as it will involve tackling issues that were set aside during the past few months' deliberations as being too hard to solve.

At some stage, say sources, those negotiations will have to tackle suspected military aspects of the nuclear programme that go back years and have never been clarified, concerning the Parchin military complex, for example.

Western diplomats say that the Geneva deal was achieved in the nick of time as Iran's enrichment capacity and its stockpiles of enriched uranium were escalating at such a rate that the country would soon have had the capacity to assemble nuclear weapons in a matter of weeks if it had chosen to break out of the nuclear non-proliferation treaty.

"It is a first important step," said the senior diplomat of the weekend agreement. "If we had not been able to agree that step and the Iranian programme had progressed the way it has been progressing in the last months, this would have significantly increased the break-out capability."

Fabius assured Israel that Paris would be protecting its security in the Middle East, but said he did not think Tel Aviv would seek military action against the Islamic republic because, if it did, "no one would understand it".

Israel's prime minister, Binyamin Netanyahu, has called the Geneva agreement an "historic mistake". He announced on Monday that he would be sending a team to Washington to discuss the Iran deal.

"I spoke last night with President Obama. We agreed that, in the coming days, an Israeli team led by the national security adviser, Yossi Cohen, will go out to discuss with the United States the permanent accord with Iran," he said.

But Britain's foreign secretary, William Hague, told parliament on Monday : "We would discourage anybody in the world, including Israel, from taking any steps that would undermine this agreement and we will make that very clear to all concerned.

"The fact we have achieved for the first time in nearly a decade an agreement that halts and rolls back Iran's nuclear programme should give us heart this work can be done and that a comprehensive agreement can be attained."

Iran's negotiating team, led by its foreign minister, Mohammad Javad Zarif, returned home on Sunday night from Switzerland to a hero's welcome at Tehran's Mehrabad airport.

Upon arriving in Tehran, Zarif updated his Facebook page, which has been "liked" by 700,000 people, apologising to his supporters that bodyguards did not allow him to spend time with them at the airport.

"It is 10:45pm Sunday night. Just arrived at home. Before posting a report drafted in airplane, I would like to thank all present in airport for welcoming us," he wrote. "I am very sorry that our guardsmen wouldn't let me get out of the automobile."

His message post, Zarif talked about the tensions behind the smiles and laughs shown on camera worldwide. Zarif said: "The art of a diplomat is to conceal all the turbulences behind his smile." He called on his critics in Iran to be fair and consider the country's national interests. "You should be alert that Zionists and other warmongers are all extremely on edge and they would spare no pretext and device to bring a deal – dubbed a deal of the century for Iran – to nothing," he wrote.

Zarif's smiling face dominated the front pages in Tehran, with two reformist newspapers, Etemaad and Shargh, publishing the picture of his handshake with his American counterpart, John Kerry.

Conservative newspapers also ran headlines suportive of Zarif's diplomacy, apart from Kayhan, a hardline newspaper whose director is appointed by supreme leader Ali Hosseini Khamenei. "The US is not to be trusted," read its deadline.

Sadeq Zibakalam, a prominent analyst at Tehran University, told Deutsche Welle's Persian service: "Geneva showed that people in Iran are tired of radicalism. We will see more newspapers in stands, less censorship by the cultural ministry and release of more political prisoners."

Zibakalam said he thought the house arrest of opposition leaders Mir Hossein Mousavi, Mehdi Karroubi and Mousavi's wife, Zahra Rahnavard, would also be lifted in the coming months.

Iran's currency market reacted positively to news of the nuclear accord, with the Iranian rial steadily recovering its value against the US dollar.