Democratic presidential frontrunner Hillary Clinton expressed firm support for the nuclear accord with Iran, saying it was flawed but still "strong".
Former US vice president Dick Cheney blasted the Iran nuclear deal as "madness" and said it marked a "capitulation" by world powers.
US Defense Secretary Ashton Carter offered assurances that the Iran nuclear deal will leave Washington with a "more effective" military option if that becomes necessary.
US Secretary of State John Kerry made a late bid to broaden backing for the Iran nuclear deal.
Britain's foreign secretary reopened his country's embassy in Tehran in a long-awaited step signalling better relations four years after a mob stormed the compound, forcing its closure.
Excess stockpiles of enriched uranium of Iran may be stored at the international nuclear fuel bank in Kazakhstan.
The fate of Iran's nuclear deal with world powers is still not decided but it will not leave the country vulnerable to US influence, supreme leader Ayatollah Ali Khamenei said.
US Secretary of State John Kerry called his Russian counterpart Sergei Lavrov on Thursday to express concern about a visit to Moscow by the commander of Iran's covert forces.
Iran's Foreign Minister Mohammad Javad Zarif met embattled Syrian President Bashar al-Assad in Damascus, and called on regional countries to "fight terrorism and extremism".
If the United States cancels the Iran nuclear deal, the blow to its credibility may be such as to hasten the end of the dollar's reign as the world's reserve currency.
Iranian Foreign Minister Javad Zarif's scheduled visit to Turkey on Tuesday has been postponed.
US President Barack Obama has predicted that opposition to his nuclear deal with Iran will erode as the agreement is implemented and a "parade of horribles" fails to materialize.
The trial of Washington Post reporter Jason Rezaian resumed Monday in Tehran, in what could be the final hearing before a judgment is issued on whether he spied on Iran.
President Barack Obama made an aggressive case for his signature nuclear deal with Iran.
Benjamin Netanyahu personally called on US Jewish groups to thwart a White House-backed Iran nuclear deal.
US Secretary of State John Kerry said there was "no question" the Iran nuclear deal will make the Middle East safer if implemented, as he sought to win over sceptical allies.
Top US military officers sought to reassure worried lawmakers that US forces would check Iran's "malign" influence in the Middle East should Congress greenlight the nuclear deal with Tehran.
French Foreign Minister Laurent Fabius arrived in Iran and said it was time to kickstart relations between the two countries after a nuclear deal made such a change possible.
The Iran nuclear deal is not intended to push Tehran's regime to reform but to prevent it building a bomb, Secretary of State John Kerry told skeptical US lawmakers.