The White House said on Friday there was a "credible prospect for a comprehensive deal" with Iran over its nuclear program that made it necessary to extend talks with Western powers another four months.
"This extension will allow us to continue the negotiations while ensuring that the progress of Iran's nuclear program remains halted during the negotiations," White House spokesman Josh Earnest said in a statement.
"We have an opportunity to achieve a lasting, diplomatic solution that will resolve one of the most pressing national security issues of our time. We will not accept anything less than a comprehensive resolution that meets our objectives, which is why it is necessary for negotiations to continue."
(Reporting by Jeff Mason; Editing by Eric Beech)