WASHINGTON — Iran's insistence that UN Security Council resolutions on its nuclear program be lifted at the front end of a final nuclear deal has emerged as an unexpected sticking point in the negotiations, diplomats say.

Western diplomats said if a final nuclear deal is reached, the United States and European Union would quickly waive and then lift unilateral, proliferation-related economic sanctions on Iran that would provide a rapid windfall to Iran's economy. (However, the US trade embargo on Iran, enacted after Iran's 1979 seizure of the US Embassy and hostage crisis, would remain in place, a senior US official said.) A new UN Security Council resolution outlining the deal and what steps all sides had agreed on would also be passed, Western diplomats said.

But the lifting of UN Security Council sanctions on Iran's nuclear program would be step by step and tied to Iran's compliance with the terms of the deal, as well as cooperation with the International Atomic Energy Agency (IAEA) probe into past possible military dimensions of Iran's nuclear program, the Western diplomats said.

Iran insists on the lifting early on of UN Security Council resolutions, which Iran sees as legitimating the international sanctions regime imposed on it for its nuclear program.