Comments by Iranian President Hassan Rohani that his government would never develop nuclear weapons have sparked world reaction.
U.S. Secretary of State John Kerry said Rohani's comments on September 18 to U.S. NBC television were positive, but cautioned that "everything needs to be put to the test."
That message was echoed by White House spokesman Jay Carney.
"There have been a lot of very interesting things, said out of Tehran and the new government, and encouraging things but actions are more important than words," Carey told reporters in Washington on September 19.
"And one of the reasons why we are seeing this change in rhetoric, we believe, is because, oh we know, is because of the international consensus that has been established with the president's leadership behind the proposition that Iran must give up its nuclear weapons program and that consensus has been backed with the most severe sanctions regime in history."
Carey reiterated that President Barack Obama has been open to talks with Tehran since he came into office.
"It has long been the position of President Obama since he was a candidate and this was a matter of debate during the Democratic primaries in 2008 as well as during the general election, that he would, as president be willing to have bilateral negotiations with the Iranians, provided that the Iranians were serious about addressing the international community's insistence that they give up their nuclear weapons programs. That is the position that we hold today," Carey said.
Earlier on September 19, NATO Secretary-General Anders Fogh Rasmussen said he was "very encouraged" by Rohani's interview with NBC News, including remarks that he has the authority to negotiate a deal with the West on Iran's controversial nuclear program.
"If what we have seen from the new Iranian president is an indication of a desire to engage in a more positive way with the international community, I could only welcome it," Rasmussen said.
However, Israeli Prime Minister Benjamin Netanyahu said Rohani's pledge not to pursue nuclear weapons was an Iranian attempt to deceive the world.
In a statement, Netanyahu said, "This same Rohani has deceived the international community in the past," an apparent reference to the time when Rohani was Iran's top nuclear negotiator.
Israel, along with many Western countries, suspects Iran is secretly developing nuclear weapons, a charge Iran has denied.
UN Secretary-General Ban Ki-moon, meanwhile, commended Rohani for his efforts to engage with the international community.
Rohani's interview on September 18 came the same day that Iran released about a dozen political prisoner, a move Ban also welcomed.
Ban was speaking on September 19 after talks at the UN with Iranian Foreign Minister Mohammad Javad Zarif, who is in New York ahead of the UN General Assembly starting next week. Rohani is due to address the General Assembly on September 24.
Ban said he would meet Rohani next week to "discuss all the matters of regional concern very closely."
Meanwhile, France's president, Francois Hollande, said he would meet Rohani on the sidelines of the General Assembly, the first meeting between presidents of the two countries since 2005.