The Obama administration is holding conversations with a range of international partners on increased sanctions on Iran as the year-end deadline for Teheran to respond to US outreach looms. While Iranian President Mahmoud Ahmadinejad only dug in his heels this week - saying that the US and its allies can set "as many deadlines as they want, we don't care" and that he was not moved - the US is stressing the upcoming deadline is serious and should be respected. "Mr. Ahmadinejad may not recognize, for whatever reason, the deadline that looms, but that is a very real deadline for the international community. And I think all of those involved in the P5+1 would encourage Iran to take that deadline as seriously as it's being taken by us to live up to their responsibilities," said White House spokesman Robert Gibbs, referring to the negotiating group composed of the UN Security Council's permanent members (the US, Russia, China, France and Britain) and Germany. Yet despite that warning, American officials are reluctant to talk about specific measures under consideration, and the US State Department notes that diplomacy still remains the preferred course of action. "President Obama has made it clear that the United States seeks engagement with Iran on the basis of mutual respect and wants to resolve international concerns about Iran's nuclear program through diplomatic means," a State Department official told The Jerusalem Post. In addressing what comes next, Gibbs put further sanctions efforts in the context of working with the UN Security Council, which is set to begin once the new rotating members join on January 1. "Discussions have been had with leaders about those next steps at the UN," he said. "We've begun to take those steps." And State Department spokesman P.J. Crowley on Tuesday said that a phone call held between representatives of P5+1 countries was looking at that process. "This call today was part of our ongoing consultation to both express what we're thinking, hear from other countries that play a critical role, particularly within the UN Security Council, about the path forward," he said, noting that he doesn't expect anything "dramatic" to be handed down on January 4, when officials return from the New Year's weekend. "The Obama administration is beginning to understand that the [rejection] of all those overtures [means] Iran's willingness to talk is really in question," said Iran expert Ilan Berman. But he added that the administration hasn't figured out which path it wants to pursue next. "We're approaching a moment of truth of sorts for the Obama administration," said Berman, vice president of the American Foreign Policy Council, who explained that the White House needs to decide whether it goes with another set of light sanctions or whether it makes a "whole-hearted effort" to keep Iran from acquiring nuclear weapons. Berman said that the latter path would mean "economic warfare," enhancing current efforts at limiting its access to foreign financial institutions and currency, the imposition of sanctions to bar foreign gasoline exports to Teheran as Congress is considering, expanding the energy sanctions to natural gas, shutting off the Iran Revolutionary Guard Corps from major markets and other large-scale moves. Alternatively, he said, another Security Council resolution would all but certainly take a limited course, and he predicted that would have little effect. "Three rounds haven't made a dent in Iran's nuclear ambitions and a fourth one isn't likely to either," said. Israel made clear what it would like to see happen Wednesday, with Prime Minister Binyamin Netanyahu emphasizing the need for serious sanctions in order to confront the Iranian nuclear threat. "We are operating with vigor to make a difference so that the international community will adopt sharp sanctions against Iran... We won't reveal everything but this is a very broad operation," he told the Knesset plenum. As to the effectiveness of sanctions and when they may take effect, Netanyahu said, "Time will tell if [sanctions are] enough - to stop the Iranian nuclear program. I estimate that the decision pertaining to this, at least in the UN, will take effect in the beginning of the year."