Secretary of State John Kerry on Tuesday said a final nuclear deal with Iran would likely allow that country to enrich uranium in some capacity, a nonstarter for many lawmakers.

The Obama administration is seeking to convince Congress to delay new sanctions on Iran, arguing they could derail diplomatic talks. Rep. Michael McCaul (R-Texas) told Kerry he could assuage the concerns of Congress and Israel by making sure a final deal precludes Iran from enriching uranium on its own soil.

“That deal was on the table a hundred years ago,” Kerry answered. “But that deal, I’m afraid, has … been lost.”

Kerry said language in an interim deal reached last month in Geneva calls for a final deal in six months that would allow some Iranian enrichment within “mutually agreed parameters” for “practical needs,” such as medical research and power generation. He said such a deal would make the U.S. and Israel safer.

“At the end of this, I can’t tell you they might not have some enrichment,” Kerry said, “but I can tell you with certainty it will not be possible for them to be able to turn that into a weapons program without our knowing it … far in advance.”

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