International negotiators are worried that Iran is using its nuclear development program as a cover for developing nuclear weapons and they have imposed economic sanctions on Tehran. Iran denies the charge, saying it is only interested peaceful nuclear programs like producing power. After a frenetic six days of diplomacy in Vienna, negotiators agreed Monday to nail down by March 1 what needs to be done by Iran and the six world powers it is negotiating with and by when. A final agreement is meant to follow four months later. Comments by key players in the talks suggested not much was agreed on in Vienna beyond the decision to keep talking. The next negotiating round was set for December but the venue is unclear. The decision appears to benefit Iran. Its nuclear program is left frozen but intact, without any of the cuts sought by the U.S. And while negotiations continue, so will dole-outs of monthly $700 million in frozen funds that began under the temporary nuclear deal agreed on late last year that led to the present talks. British Foreign Secretary Philip Hammond said the sides were giving themselves until March to agree on a text "that sets out in layman's language what we have agreed to do." Experts then will be given another four months to "translate that into precise definitions of what will happen on the ground," he told reporters. Even the new deadline for a final deal was not immediately clear, with negotiators saying it was July 1, and Hammond fixing it at June 30. Hammond and other foreign ministers of the six powers sought to put a good face on what was achieved. Hammond spoke of "significant progress," while German Foreign Minister Frank-Walter Steinmeier said only differences about "technical details" remained. But the length of the extension suggested that both sides felt plenty of time was needed to overcome the disputes on how much Iran needed to restrict nuclear activities that could be used to make weapons in exchange for relief from sanctions imposed over its nuclear program. "All the people involved here feel that there really is a chance to find out a way to each other and we are going to take that chance," Steinmeier said about the decision to extend. But obstacles far from the negotiating table could complicate the process. Members of the new Republican-controlled U.S. Congress that will be sworn in in January have already threatened to impose additional sanctions on Iran and may well have enough votes to overturn an expected veto of such legislation by President Barack Obama. New sanctions could very well derail the talks, as Iran has signaled they would be a deal breaker. In Tehran, hardliners fearful that their country could give away more than it gets under any final deal could increase pressure on Supreme Leader Ayatollah Ali Khamenei to break off talks. The talks extension, however, appears to have the approval of Khamenei, who is the ultimate arbiter in his country.