The U.S. and other world powers may need to vigilantly inspect Iran's nuclear facilities for 20 years to fully dismantle its nuclear weapons program, according to a new report by a Washington think tank.

Iran currently has 20,000 centrifuges enriching uranium and would need to reduce that number to 4,000 to demonstrate that its program is only intended for energy purposes and not aimed at enriching enough uranium to make a nuclear bomb, according to a new report by the Institute for Science and International Security provided to the Wall Street Journal.

In order to fully disable its weapons capability, Iran also would need to shut down an underground uranium-enrichment site, convert a heavy-water reactor and agree to a 20-year inspections regime, ISIS said in its report.

The report demonstrates just how difficult it will be for the U.S. and like-minded world powers to reach their long-term goal of assuring that Iran does not have the capability to develop nuclear weapons.

The International Atomic Energy Agency, the world body charged with inspecting Iran's nuclear sites, said Monday that Iran began scaling back its nuclear activities before the Jan. 20 start date to a six-month interim deal reached with the United States, United Kingdom, France, Germany, Russia and China.

Over the next six months, the international community will test Iran's compliance with the requirements laid out in the agreement with the goal of reaching a permanent deal with Tehran.

But Iranian officials' public statements are rattling Western officials and lawmakers worried about lifting sanctions on Tehran that are difficult to reinstate in exchange for easily reversible concessions on enriching uranium.

President Hassan Rouhani took to Twitter in early January to state that the west surrendered to Iran's "will" in the deal, and days later Iran's top nuclear negotiator, Abbas Araghchi, said Tehran can resume enriching uranium to 20 percent levels within one day if it so desires.

Even as they hailed Iran's early compliance with the preliminary deal, Obama administration officials on Monday said they are fully aware of the challenges of reaching a long-term deal.

“These actions today are significant steps in our efforts to achieve a diplomatic solution to prevent Iran from obtaining a nuclear weapon,” said State Department spokeswoman Jen Psaki. “The coming negotiation to reach a comprehensive agreement that addresses all of the international community’s concerns will be even more complex, and we go into it clear-eyed about the difficulties ahead,” she said.

This story was published at 9:44 a.m. and has been updated.