UN Secretary-General Ban Ki-moon hailed the exchange of prisoners and the lifting of sanctions against Tehran, saying the two countries should now cooperate on additional challenges to find "a safer future"
President Barack Obama on Sunday heralded the implementation of a nuclear deal with Iran, saying world powers had cut off every path Tehran had to a nuclear bomb and that a prisoner swap showed what was possible with diplomacy.
"This is a good day because once again we are seeing what's possible through strong American diplomacy," Obama said at the White House, adding that Iran would not "get its hands" on a nuclear weapon.
"These things are a reminder of what we can achieve when we lead with strength and with wisdom."
His remarks were an implicit rebuke to Republicans, who have criticised the president for his engagement with a country that has long been an enemy of the United States.
The president said the United States still had significant differences with Iran and would continue to enforce sanctions against its ballistic missile program.
"Even as we implement the nuclear deal and welcome our Americans home, we recognise that there remain profound differences between the United States and Iran. We remain steadfast in opposing Iran's destabilising behaviour elsewhere," he said.
The president described the release of six Iranian-Americans and one Iranian charged in the United States as a "reciprocal, humanitarian gesture" that was a one-time event.
He also said a settlement between the United States and Iran at The Hague, in which Iran received $400 million in funds frozen since 1981 plus $1.3 billion in interest, would save US money. There was no point in dragging out that dispute, he said.
Obama campaigned for the White House in 2008 on a promise to engage with US enemies including Iran and Cuba. The nuclear pact and warming relations between Washington and Havana are likely to become a big part of his legacy as he completes his final year in office.
Obama said he was hopeful the events signalled an opportunity for Iran to work more cooperatively with the rest of the world.
UN Secretary-General Ban Ki-moon hailed the exchange of prisoners by the United States and Iran and the lifting of sanctions against Tehran, saying the two countries should now cooperate on additional challenges to find "a safer future".
"I commend the moves by the governments of both countries to improve ties. I am also heartened by the lifting of sanctions against Iran," he said on a visit to Dubai, adding he hoped the parties honoured a nuclear deal that made possible the lifting of curbs.
"Now is the moment to push for cooperation on other pressing challenges through dialogue which should continue to find a way for a safer future," he said.