Foreign Secretary William Hague has spoken to an Iranian minister for the first time in over a year, indicating Britain's openness to better relations with the country.
In a phone call with foreign minister Ali Akbar Salehi, Mr Hague reiterated the need for urgent progress to resolve the international community's concerns about Iran's nuclear programme.
But the Foreign Office (FCO) said Mr Hague made it clear that Britain was open to improvements in its relationship with Iran "on a step-by-step and reciprocal basis".
The election of relatively moderate president Hassan Rouhani in June has raised the prospect of a thaw in Tehran after years of confrontation with the international community under unpredictable hardliner Mahmoud Ahmedinejad.
Mr Hague did raise the case of British-Iranian national Abbas Yazdi who reportedly went missing in Dubai in June.
His wife is quoted in reports as saying she fears he has been kidnapped by Iranian intelligence officers and taken to Iran.
An FCO spokesman said: "A British national Mr Abbas Yazdi, was reported missing in Dubai, where he is normally resident, on 25 June. We are in contact with the Dubai authorities. We are providing consular assistance to the family at this difficult time."
The Foreign Secretary also said he was willing to meet the Mr Salehi during the UN General Assembly in New York in September.
The last time Mr Hague spoke to an Iranian minister was at an event in Kabul, Afghanistan, in June 2012, an FCO spokesman said.