William Hague has hailed an historic nuclear agreement between Western powers and Iran as "good news for the whole world".
An interim deal to restrict Iran's nuclear programme was finally reached after five days of top-level talks in Geneva, Switzerland on Sunday.
Listen to William Hague discuss the deal on Radio 4...
But the Israeli Prime Minister Benjamin Netanyahu said the deal was a "historic mistake".
He added: "Today the world became a much more dangerous place because the most dangerous regime in the world made a significant step in obtaining the most dangerous weapons in the world".
Writing on Twitter after the agreement, Hague said: "Important and encouraging first stage agreement with Iran. Nuclear programme won't move forward for six months and parts rolled back."
He continued: "This agreement shows it is possible to work with Iran, and through diplomacy address intractable problems.
"Tonight's agreement with Iran good for the whole world, including Middle Eastern countries and the people of Iran themselves.
"Negotiations were painstaking. Tomorrow hard work begins of implementing and building on the agreement."
Hague and negotiators from US, France, Germany, Russian and China have been in talks with Iran since Wednesday.
President Barack Obama hailed the deal as an "important first step" and "new path" towards a more secure world and addressing concerns over its nuclear programme.
Speaking from the The White House the president said the deal included "substantial limitations" on Iran, cutting off its ability to make a nuclear bomb.
Obama said: "While today's announcement is just a first step, it achieves a great deal.
"For the first time in nearly a decade, we have halted the progress of the Iranian nuclear programme, and key parts of the program will be rolled back."
Under the terms of the deal, Iran agreed to halt progress on key elements of its programme in exchange for modest relief from certain economic sanctions.
Hague said the agreement was an "important moment" that had been "well worth bringing about".
He told Sky News that the deal allowed for "proportionate and limited relief from sanctions" for Iran that would involve the unfreezing of some assets and the lifting of suspensions of some sanctions on items like petrochemicals, gold and precious metals.
In return Iran will have to carry out actions agreed through the interim deal, including stopping the enrichment of uranium above a level of 5% and the elimination of the stockpile of uranium above that level that it has already built up, as well as stopping work on its heavy water reactor at Arak.
Hague said: "The great bulk of sanctions will remain in place until there is a comprehensive and final agreement that gives the world the necessary assurances that, for the future, Iran's nuclear programme is exclusively for peaceful purposes."
The challenge now, he said, is making sure the agreement is implemented fully, and paving the way for a comprehensive and final deal.
"The UK and our partners will implement this in good faith, we look to Iran to implement it in good faith, and then there is the whole issue of a comprehensive and final settlement, one in which the world can be sure that the development of a nuclear programme in Iran is for peaceful nuclear energy in the future and in which all sanctions are lifted."
He added: "This is a very important change, that it is possible to agree with Iran about these matters, that the political will from all sides has been there. And that is something that many people would have doubted only a few months ago."
The West has long held concerns about Iran's nuclear ambitions, harbouring fears that it has been harnessing powers to develop nuclear weapons.
But Tehran insists that it is enriching uranium only for reactor fuel, medical uses and research.
With an interim six-month deal now in place both sides will have freedom and confidence to work towards the goal of a long-term agreement.
Outlining terms of the deal, President Obama said the progress of the Iranian nuclear programme had been "halted", with key parts "rolled back".
As well as the stopping levels of enrichment and eliminating stockpiles, Iran is also banned from using its new centrifuges for enriching uranium, nor install or start new ones, and production of centrifuges will be limited.
New inspections of Iran's nuclear facilities will also allow the international community to check that Tehran is fulfilling its commitments.
Obama said they were "substantial limitations which will help prevent Iran from building a nuclear weapon".
And he said that while the West will refrain from imposing new sanctions, if Iran reneges on its commitments "we will turn off the relief and ratchet up the pressure".
He added: "Iran, like any nation, should be able to access peaceful nuclear energy. But because of its record of violating its obligations, Iran must accept strict limitations on its nuclear program that make it impossible to develop a nuclear weapon."
US secretary of state John Kerry told reporters that if Iran's nuclear programme was for peaceful purposes only, then it needed to "prove it" to the world, and said the deal would make Israel safer.
Iran's foreign minister Mohammad Javad Zarif insisted his country had an "inalienable right" to enrich uranium. But he said the agreement was an important first step to putting an end to a "rather sad chapter".
He said: "I believe it is important that we all of us see the opportunity to end an unnecessary crisis and open new horizons based on respect for the rights of Iranian people and removal of any doubts about the exclusively peaceful nature of Iran's nuclear programme.
"These have been and will remain our objective and I am confident that through co-operation we can move forward.
"This is only a first step. It is an important achievement, but this is a first step. We need to work together based on the same principles on which we started, principles of equal footing, mutual respect and common benefit, so that we can put an end to this unnecessary and rather sad chapter."
He added: "I hope that as we go along we can start restoring the lost confidence. The Iranian people demand respect for their rights but demand respect for their dignity."
Israel prime minister Benjamin Netanyahu has criticised the deal, saying the international community has given up too much to Iran.
In a joint statement with Zarif, the EU's High Representative Baroness Ashton, who brokered the deal, said: "The adoption of the joint plan of action was possible thanks to a sense of mutual respect and a determination to find a way forward which is beneficial for all of us."
Kerry and Hague will have talks in London today on the Middle East, the US State Department said yesterday.
As well as further discussions on Iran, they are expected to consider the latest developments in Syria and the Middle East peace process.