UPDATE 5:27 EDT: British Foreign Minister Phillip Hammond issued a joint statement in London Saturday on behalf of his American, French, German and EU counterparts, citing "substantial progress" in negotiations with Iran this week. The diplomats flew to London Saturday to discuss how to move forward into the last week of talks before a self-imposed March 31 deadline to come to a political agreement with Iran.

"We agreed that substantial progress had been made in key areas although there are still important issues on which no agreement has yet been possible," Hammond said, according to Reuters. He added, "Now is the time for Iran, in particular, to take difficult decisions."

Original Story:

American and Iranian officials cited progress Saturday in the multiparty negotiations to strike a historic deal that would curb Iran's nuclear program in exchange for an end to economic sanctions on the country. U.S. Secretary of State John Kerry, who is leading the American delegation at the talks in Switzerland, emerged with hopeful words ahead of a self-imposed March 31 deadline to draft a preliminary political agreement between the parties.

Sanctions placed on the Islamic Republic by the U.S., United Nations and European Union over the years have largely crippled Iran's economy, which also has been hit hard by the collapse in crude-oil prices since the middle of last year.

"We are not rushing ... but we recognize that fundamental decisions have to be made now, and they don't get any easier as time goes by. It is time to make hard decisions," Reuters quoted Kerry as saying in Lausanne. The secretary of state added, "We have the opportunity to try to get this right."

In the negotiations, Iran is on one side and the P5+1 group is on the other side. The group consists of the five permanent members of the U.N. Security Council -- China, France, Russia, the U.K. and the U.S. -- plus Germany. The parties gave themselves a June 30 deadline to ink a final agreement over Iran's nuclear program.

Kerry is scheduled to travel to London to meet with French, German, British and other EU representatives to solidify a position in advance of the resumption of talks next week. 

Iranian officials contend their nuclear program has peaceful purposes, and they are reluctant to give it up. The anti-Israeli rhetoric often heard from Iranian leaders has many Western politicians concerned the nation is seeking a nuclear weapon to use against Israel.

Despite the lack of a deal this week, Iranian President Hassan Rouhani echoed Kerry's optimism in remarks to the official Islamic Republic News Agency Saturday. "There is nothing that cannot be resolved," said Rouhani, adding that "shared points of view emerged in some of the areas where there had been a difference of opinion, which can be a foundation for a final agreement."

Both the American and Iranian leaderships are under intense pressure from more hawkish politicians back home.

On the one hand, Congressional Republicans in the U.S. have been highly critical of President Barack Obama administration's willingness to negotiate with Iran. They are concerned it will reach an unfavorable deal that would allow Iran to develop a nuclear weapon, and they have threatened to fight such any such deal. U.S. Sen. Lindsey Graham, R-S.C., has vowed to cut funding for the U.N. should he and his colleagues not like the deal Obama inks with Iran.

On the other hand, Iran's Supreme Leader Ayatollah Ali Khamenei, whose cooperation will be necessary for an agreement, was also publicly critical of the U.S. in remarks Saturday. Amid shouts of "Death to America" during a speech in the northeastern city of Mashhad, Khamenei accused the U.S. of using economic pressure and "bullying" in an attempt to turn Iranians against Islamic rule, Reuters reported. He told the crowd, "Of course, yes, death to America, because America is the original source of this pressure. They insist on putting pressure on our dear people's economy. What's their goal? Their goal is to put the people against the system."