Britain and Iran will reopen their respective embassies in the coming days, an Iranian official said Thursday, four years after their closure when protesters angry over nuclear sanctions stormed the UK mission in Tehran.

The official said Foreign Secretary Philip Hammond, who helped negotiate a historic deal between Iran and the West on the Islamic republic's nuclear programme, "will travel Sunday to Iran for the reopening of the British embassy".

"At the same time" Tehran would reopen its embassy in London, the official told AFP, without providing a specific date.

The Foreign Office confirmed Hammond would be visiting Iran in the coming days but did not mention the reopening of the embassy.

Hammond would be the first British foreign secretary to visit Iran in more than a decade.

Several European officials have travelled to Tehran since July 14, when Iran struck the nuclear agreement with Britain, China, France, Germany, Russia and the United States.

The accord, which ended a 13-year standoff, will see the lifting of economic sanctions imposed on Iran and has sparked a flurry of interest from countries seeking to re-connect with oil-rich Iran.

In November 2011, hundreds of Islamist demonstrators protesting against Western sanctions stormed and ransacked the British embassy in Tehran.

Britain ordered its embassy in Tehran closed after the assault and expelled Iranian diplomats from London.

- Post-Rouhani election thaw -

During the assault on the British embassy four years ago, protesters tore down the Union Jack, ripped up pictures of Queen Elizabeth II, trashed embassy offices and set documents alight.

At the time Britain accused Iran of failing to protect the mission.

The assault also sparked condemnation from the UN Security Council, and some European countries recalled their envoys for consultations.

According to the British newspaper The Guardian, Hammond will reopen the embassy in Tehran on Sunday.

Hammond will be accompanied by a business delegation to Iran where the reopened embassy will be staffed by a small team at first, including non-resident charge d'affaires Ajay Sharma, said the paper.

Sharma had been appointed to the post in November 2013 at the same time as Iran named a non-resident envoy to Iran, in a move to normalise ties even as their embassies remained closed.

That thaw had come about after the June 2013 election in Iran of President Hassan Rouhani, a reputed moderate who had reached out to the West from the early days of his presidency.

Plans to reopen the British embassy and the one in London had been in the works since last year and the nuclear deal has proven a catalyst for Iran to restore its ties with the world.

On July 16, British Prime Minister David Cameron expressed an interest in reopening the embassy during a telephone conversation with Rouhani.

And later that month Britain lifted an official warning against all but essential travel to Iran, with Hammond citing "decreasing hostility under President Rouhani's government".

Almost all of Iran is now marked "green" in the government's foreign travel advice, though border areas with Iraq, Pakistan and Afghanistan remain "red", a warning against all travel.

And with the international community lifting decades of crippling sanctions, this could encourage travel to Iran particularly by businessmen in quest of investing in the Islamic republic which needs to revamp its battered economy.

Hammond's visit to Tehran will be the latest by a top European diplomat, following in the footsteps of his Italian, French and German counterparts who travelled with business delegations.

Europe is keen on renewing trade ties with Iran and most countries have diplomatic representation in Iran.

But the United States, which led the nuclear talks with Iran, has no diplomatic relations with Iran since 1979 following the 444-day hostage crisis that followed the storming of its Tehran embassy.