Iran knows it will face "tremendous costs and consequences and implications" if it tries to develop a nuclear weapons, said the head of the U.S. Central Intelligence Agency. John Brennan, speaking on Fox News Sunday said he believed Iran was aware of what would happen if it moved ahead with a nuclear weapons program. He said he was confident that U.S. intelligence capabilities were sufficiently robust and that the United States understood what Iran's nuclear program entailed. He spoke a day after U.S. Secretary of State John Kerry held meetings in Europe during a temporary pause in nuclear talks with Iran. In London, the British, French and German ministers and Kerry said while substantial progress has been made in key areas, there were still important issues on which no agreement has been possible. They called on Iran to make what they called difficult decisions and said they could not sign on to a deal that was not "comprehensive, durable and verifiable." Before those talks, Kerry said, "Fundamental decisions have to be made now." He said making those decisions did not get any easier as time went by. President Barack Obama said in an interview posted Saturday by the Huffington Post that the question was whether Iran was prepared to show the world it was 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 is the possibility," he said. The talks are set to resume this week in Lausanne, Switzerland, with diplomats from China and Russia joining in. They are the other two members of the so-called P5+1 nations negotiating with Iran. Earlier Saturday, Iranian President Hassan Rouhani acknowledged that differences remained, but said "there is nothing that cannot be resolved." He said in a Persian New Year message to the Iranian people that foreign powers have learned that the best way to deal with Iran was with "respect" instead of "threats and sanctions." The parties have a March 31 deadline for a framework agreement. Iran would limit its uranium enrichment to prevent it from building a nuclear bomb. In exchange, the world powers would lift the sanctions that have wrecked the Iranian economy. Iran denies wanting a bomb and insists its nuclear program is for peaceful civilian purposes.