Senators will press the Obama administration on Thursday to get tougher on enforcing limits on Iran as officials prepare to lift U.S. sanctions that have helped cripple the Iranian economy.

The Senate Foreign Relations Committee is expected to hear from Stephen Mull, the State Department official charged with implementing the nuclear deal with Iran, on the administration's plan to hold the Shiite Muslim theocracy in Tehran to its terms. Thomas Countryman, assistant secretary of state for international security and nonproliferation, and retired Air Force Lt. Gen. Frank Klotz, head of the National Nuclear Security Agency, also are expected to appear.

The administration is expected by the end of the week to certify that Iran is complying with the deal reached July 14 in Vienna that sets limits on Iranian nuclear activities in exchange for sanctions relief. But there's widespread skepticism among Democrats and Republicans in Congress that Iran will hold to the agreement, fueled by the administration's lack of response to such provocations as the testing of advanced, nuclear-capable ballistic missiles banned by U.N. sanctions that will stay in place for eight more years.

Lawmakers are most concerned about the International Atomic Energy Agency's decision Tuesday to close the file on Iran's past nuclear work, even though a report said Iran had experimented with trying to build a nuclear weapon through 2009, later than had been previously thought, and was not as conclusive as many had expected.

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