U.S. President Barack Obama says U.S. intelligence estimates show Iran is "a year or more away" from building a nuclear weapon.
In an interview with the Associated Press, Obama acknowledged that U.S. estimates were more conservative than those of Israel, which said Iran was much closer that that to building an atomic weapon.
President Obama also said the world must test whether Iran's President Hassan Rouhani was serious about resolving its nuclear dispute diplomatically.
His comments come after he held a short phone conversation with Rouhani on September 20, in the first direct contact between the two countries' top leadership in more than three decades.
The contact capped a week of outreach to the West by Rouhani and Iranian Foreign Minister Javad Zarif, during the annual opening session of the U.N. General Assembly.
On Saturday, Iran's supreme leader voiced support for Rouhani's overtures to the West, but he said some aspects of his trip to New York last month were "not appropriate."
In remarks posted on his website, Ayatollah Ali Khamenei did not elaborate on his objections, but it would appear they center on Rouhani's conversation with Obama.
The ayatollah said the U.S. government was not trustworthy and broke its promises.
The commander of Iran's elite Revolutionary Guards, General Mohammad Ali Jafari, called Rouhani's decision to engage in the phone conversation a "tactical mistake."
The issue underlying the two presidents' conversation - and most all other aspects of the arms-length relationship between Washington and Tehran - concerns Western efforts to resolve the standoff with Iran over its nuclear development program. I
ran has insisted its nuclear work is purely for peaceful purposes, but the U.S. and many of its allies disagree, contending that Iran has embarked on a secret program to build nuclear weapons, with missiles capable of striking at Israel and other countries in the Middle East.
Working through the U.N. Security Council, the U.S., Britain, France and others have imposed several rounds of sanctions that have badly battered Iran's economy.
Some information for this report was provided by AP.