Britain, France, Germany, and the United States have affirmed their "unity of purpose" in the Iran nuclear talks, saying the Islamic Republic had to take "difficult decisions."
The Western powers’ top diplomats met in London on March 21 to discuss progress in negotiations with Iran over its nuclear program.
Reading a joint statement after the meeting, British Foreign Secretary Philip Hammond said, "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."
Delegates from Iran and six world powers -- the United States, Britain, France, Germany, Russia, and China -- have spent the past week in the Swiss city of Lausanne trying to reach an agreement on curbing Tehran's nuclear program in exchange for relief from economic sanctions.
A framework agreement is due by March 31 and a full deal by June 30.
In an interview with The Huffington Post published on March 21, U.S. President Barack Obama said Iranian negotiators have not made enough concessions in nuclear talks to seal an agreement.
“They have not yet made the kind of concessions that are I think going to be needed for a final deal to get done,” Obama said in the interview.
He added: “But they have moved, and so there’s the possibility.”
Iran insists that its nuclear activities are purely for peaceful purposes, but Western nations fear they could be a cover for developing nuclear weapons.
Speaking in Lausanne before leaving for London, U.S. Secretary of State John Kerry said that "substantial progress" has been made in negotiations with but that "important gaps" still stand in the way of a deal.
Kerry sought to play down rumored disagreements between the United States and France over the easing of sanctions.
"We are united in our goal, our approach, our resolve and our determination to ensure that Iran's program is entirely peaceful," he said.
Washington has reportedly proposed a gradual lifting of sanctions in return for concrete actions by Iran to curb its nuclear program, while France is reported to want only "a symbolic easing" of the sanctions imposed over the last decade.
Iran wants all sanctions to be lifted immediately, a step one of the European negotiators has described as "out of the question."
Kerry also said that while the time has come to make "fundamental decisions," Washington would not rush into a flawed agreement with Tehran.
"We don't want just any deal," he said. "If we had, we could have announced something a long time ago.
The French ambassador in Washington, Gerard Araud, earlier in the day tweeted that “making the end of March an absolute deadline is counterproductive and dangerous." The sides “need all time to finalize a complex agreement,” he added.
Kerry's comments appeared to play down optimistic remarks made by Iranian President Hassan Rohani, who voiced confidence that a final agreement could be at hand.
"In this round of talks, 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," he was quoted as saying by the Iranian state news agency IRNA.
"There is nothing that cannot be resolved," he added.
Iranian Foreign Minister Mohammad Javad Zarif said on March 20 there was "no reason" to report an agreement is at hand.
The talks in Switzerland were halted after the Iranian delegation returned to Tehran, reportedly either for the funeral of Rohani's mother or to mark Norouz, the Persian New Year.
Negotiators are due to reconvene next week to try to break the deadlock.
In a video message for Norouz, U.S. President Barack Obama told the Iranian people on March 20 that there was "an historic opportunity to resolve this issue peacefully".
But Iran's Supreme Leader Ayatollah Ali Khamenei warned on March 21 against submitting to foreign demands in order to achieve economic growth.
In his speech marking Norouz, Khamenei attacked "arrogant powers" -- a reference to major Western countries -- for what he said was their role in bringing about a fall in the oil price by more than half in recent months.
He added that Iran's "enemies" sought to turn the Iranian people against the Islamic Republic.