In a live televised statement from the White House President Barack Obama described today's deal with Iran an "important first step" and said "substantial limitations" will help prevent Iran from building a nuclear weapon.
He said that the US remained committed to "friends and allies" and said Israel had good reason to be sceptical of Iran's intentions.
When you consider the diplomatic mountain the US and Iran have already scaled, you get a daunting sense of the challenge ahead.
The deal between Iran and world powers looks like a breakthrough, but with six months of wrangling over details ahead, it could still fail.
The nuclear agreement between Western powers and Iran was broadly welcomed by politicians, former world leaders and Middle East experts.