Foreign Secretary William Hague will address MPs in the House of Commons today on the deal reached by the international community with Iran over its nuclear ambitions.
A deal struck after lengthy negotiations in Geneva, Switzerland, commits Iran to curb its nuclear activities for six months in exchange for limited and gradual relief from some sanctions, including access to £2.5 billion ($4.2 billion) from oil sales.
Israel's Benjamin Netanyahu called the agreement "an historic mistake", but David Cameron hailed the deal as an "important first step".
Prominent Iranian-Americans have praised the Iranian nuclear deal as a significant first step in what they hope will be more harmonious relations between Iran and the international community.
I don't think these negotiations are going to have an effect either on Iran's global image or on Americans' perceptions of Iran.
But they may set the groundwork for eventual normalisation between Iran and the US - and that is something which should be celebrated.
For anybody who has had direct and intimate contact with people living in Iran, the first sign of relief will be about the economics.
I know that's on many people's minds. They don't like to see their loved ones harmed.
People are now questioning Rouhani's determination to uphold the people's rights.
That's going to be one of his major challenges in the months to come - whether he stands up for his people or gives up the domestic issues to the hard-liners in Tehran.
Oil prices fell sharply today after world powers struck a landmark deal with Iran to curb its nuclear programme in exchange for an easing of international sanctions.
While Iran will not be allowed to increase its oil sales for six months, any easing of Middle East tensions tends to lead to lower crude prices.
Israel's Prime Minister Benjamin Netanyahu has called the nuclear deal with Iran "an historic mistake" and said it has "made the world a much more dangerous place".
President Obama telephoned Mr Netanyahu this evening to say the US would remain committed to Israel.
Warning: ITV News' Middle East Correspondent Geraint Vincent's report contains flash photography:
President Barack Obama has told Israeli Prime Minister Benjamin Netanyahu that he wants to begin US-Israeli consultations immediately on an effort to reach a comprehensive solution to Iran's nuclear programme, according to the White House.
Mr Obama reassured the Israeli leader that the United States will remain firm in its commitment to Israel, after Mr Netanyahu called the nuclear deal with Iran "an historic mistake".
"The president underscored that the United States will remain firm in our commitment to Israel which has good reason to be sceptical about Iran's intentions," said White House spokesman Josh Earnest.
President Barack Obama has spoken by phone with Israeli Prime Minister Benjamin Netanyahu to discuss a nuclear deal between Iran and six major powers.
The White House announced the call as Obama flew aboard Air Force One from Washington to Seattle.
Germany's Foreign Minister has welcomed a nuclear deal between Iran and six world powers in Geneva today, in what is being billed as one of the most significant developments with Iran in 30 years.
Guido Westerwelle told reporters:
The agreement of Geneva is a turning point in those difficult times and after very difficult talks. We are a step closer to our goal of preventing a nuclear armament of Iran.
Foreign Secretary William Hague has said the deal between Iran and world powers "vindicates the policy of pressure through sanctions and diplomacy through negotiations."
Warning: This video contains flash photography
The UK and US will ensure a deal on Iran's nuclear programme will be implemented and that it does not give the country any right to uranium enrichment, the Foreign Secretary said as he met with US Secretary of State John Kerry in London.
William Hague told reporters: "It is a very important opportunity for the future. And it vindicates in the future the policy of pressure through sanctions and diplomacy for negotiations in which the United State and United Kingdom have been strong partners for so long".