U.S. Secretary of State John Kerry called on Iran to make difficult decisions now to enable agreement on the future of its nuclear program by the deadline at the end of this month.

　　He told reporters in Lausanne, Switzerland, Saturday that important gaps remain in reaching an agreement. “Fundamental decisions have to be made now, and they don’t get any easier as time goes by,” Kerry said.

　　Officials made similar statements as the two previous deadlines approached and were missed. But they said it would be difficult to extend the deadline again.

　　Kerry to Iran: It Time for Tough Decisions on Nuclear Program

　　Kerry met later in London with representatives of other members of the P5+1 group that has been negotiating with Iran. Officials said that while substantial progress has been made in key areas, there are still important issues on which no agreement has been possible.

　　Kerry and the British, French and German foreign ministers said they could not sign on to a deal that was not "comprehensive, durable and verifiable."

　　President Barack Obama said in an interview posted Saturday by the Huffington Post that the question is whether Iran is prepared to show the world it is not developing nuclear weapons.

　　"Frankly, they have not yet made the kind of concessions that are, I think, going to be needed for a final deal to get done. But they have moved, and so there's the possibility," he said.

　　The talks with Iran are to resume next week in Lausanne.

　　Iran says its nuclear program is purely peaceful, and it has no interest in building a nuclear bomb.  But the United Nations — represented by the United States and five other countries in these talks — wants proof.

　　Experts say Iran is already dangerously close to being able to build a bomb, and had a program intended to do so in the past.

　　The negotiators have kept most details of their talks secret, but recent leaks indicate progress on key issues, including the number of nuclear enrichment centrifuges Iran will be allowed to operate, the timing of relief from crippling economic sanctions and, the rules covering international inspections to ensure Iran is complying with any agreement.

　　“Implementation is not based on trust, but it is based on intensive verification, on the ability to know and understand what is happening,” Kerry said in Lausanne.

　　Experts say with its current capacity to enrich uranium, Iran could build a bomb in a few months. The six countries reportedly want to reduce that capacity so they would have at least a year of warning if Iran decided to move toward building a bomb.

　　Reports in recent days indicate France is taking a tougher line on some issues than the other negotiating countries. But Kerry sought to dispel that notion.

　　“We are united in our goal, our approach, our resolve and our determination to ensure that Iran’s program is entirely peaceful,” he said.

　　Critics of the negotiations say no agreement can ensure Iran does not have a secret nuclear weapons program hidden somewhere in the country.  They also worry that after a deal expires — reportedly in 10 or 15 years — Iran will be free to expand its enrichment program and build a nuclear weapon if it wants to.

　　Key skeptics of the talks include many members of the U.S. Congress and the Iranian leadership, as well as some Middle Eastern governments, including Israel and Saudi Arabia.

　　The response to the criticism is that without an agreement that limits Iran’s nuclear program, and also satisfies some of its demands, there will be no way to stop Iran from developing a nuclear weapon, short of military action.

　　And officials warn that the nearly global sanctions that pushed Iran to the negotiating table could break down if there is no agreement, giving Iran what it wants without getting commitments on the nuclear program in return.

　　On Saturday, Kerry tried to reassure the critics, saying he does not want “just any deal” but one that is comprehensive and durable, and that all parties will uphold.

　　He said an agreement could be reached by March 31 if there is “political will and tough decision-making.”  He urged all sides to “choose wisely in the days ahead.”