U.S. President Barack Obama has said the United States would "walk away" from nuclear talks with Iran if an acceptable deal cannot be reached with Tehran.
In a television interview aired on March 8, Obama said any agreement must allow Western powers to verify that Tehran isn't going to obtain an atomic weapon.
Obama said "even if they cheated we would be able to have enough time to take action."
In the TV interview, Obama said the United States and Iran had narrowed their differences.
"We have made progress in narrowing the gaps, but those gaps still exist," Obama told CBS News', Face the Nation.
The next round of talks is set to begin March 15.
Negotiators are facing a self-imposed deadline at the end of March to reach a framework deal.
Iran dismisses Western suspicions it is using its civilian nuclear program to secretly develop a nuclear weapons program.
Senate Majority Leader Mitch McConnell, a Republican, cautioned the Democratic president not to make "the bad deal we all anticipate he's going to make."
He said Obama "cannot work around Congress forever."
McConnell told CBS on March 8 that he was hoping to get 67 of the Senate's 100 members "to assert the historic role of the Senate ... in looking at matters of this magnitude".
Sixty-seven votes are needed to overturn any presidential veto of legislation regarding an Iran deal. The same number of votes are needed for Senate ratification of treaties negotiated by presidents with foreign countries.
Arguing that Iran was "fomenting trouble" in other Middle Eastern countries including Syria, McConnell also warned that the Senate "cannot ignore all of their other behavior in looking at the potential nuclear deal."
The negotiations with Iran center on restricting its ability to produce weapons grade nuclear materials while allowing it to develop nuclear energy.