US Secretary of State John Kerry said Sunday that world powers and Iran have never been closer to an agreement to cap Tehran's nuclear program in exchange for sanctions relief, but that the negotiation could still "go either way."Speaking at a press conference in Vienna following a meeting with his Iranian counterpart Mohammad Javad Zarif, Kerry said that European foreign ministers would be returning to the Austrian capital on Sunday night "to see if we are going to close an agreement."Kerry reiterated that if the Obama administration did not get a deal that it was comfortable with, "if there is absolute intransigence" on the part of the Iranians, the US will walk away from the talks."We want a good agreement and only a good agreement," Kerry said. "We're not going to shave at the margins just to get an agreement."