The British embassy in Iran is to be reopened later, nearly four years after it was closed.
Foreign Secretary Philip Hammond will be in Tehran with a delegation of business leaders for a ceremony to mark the reopening. Iran is simultaneously reopening its embassy in London.
The UK embassy was closed in 2011 after it was stormed by protesters during a demonstration against sanctions.
Mr Hammond will be the first UK foreign secretary to visit Iran since 2003.
The visit comes weeks after Iran reached a deal with six world powers aimed at curbing its nuclear programme.
Mr Hammond said the the nuclear deal and the election of Hassan Rouhani as president in June 2013- who has pledged greater engagement with the Western World – had been “important milestones” in the improved relations between the two countries.
He said: “Reopening our embassies is a key step to improved bilateral relations.
“In the first instance, we will want to ensure that the nuclear agreement is a success, including by encouraging trade and investment once sanctions are lifted.
“Britain and Iran should also be ready to discuss the challenges we both face including terrorism, regional stability, the spread of Isil in Syria and Iraq, counter-narcotics and migration.”
Initially, the embassy will be headed by a charge d’affaires, Ajay Sharma, but Mr Hammond said an agreement on upgrading to full ambassador status is expected to be reached in the coming months.
The reopening of the embassy will be marked by a ceremony attended by Mr Hammond, Mr Sharma, and representatives of the Iranian Ministry of Foreign Affairs and the wider diplomatic community.
A trade delegation will travel to Tehran with Mr Hammond and the Exchequer Secretary to the Treasury Damian Hinds to discuss possible future trade opportunities.
In November 2011 Iran announced it was expelling the UK’s ambassador in retaliation for British support for tougher sanctions on Tehran over its nuclear programme.
Hundreds of protesters stormed embassy compounds two days later, smashing windows, torching cars and burning Union flags.
The UK responded by closing the Iranian embassy in London later that month.
But following the election of Hassan Rouhani and an agreement on how to deal with Iran’s nuclear programme, the then Foreign Secretary William Hague proposed the reopening of the embassy in June last year.
Since then, the reopening of the embassy has been held up by technical problems over visa policy and communications equipment, Mr Hammond has said.