The veteran diplomat's comments came on the same day that Mr Trump said that Washington would impose new sanctions on Iran in retaliation for its shooting down of the drone over the Strait of Hormuz on Thursday, an attack that almost pushed him into a military retaliation.
"I look forward to the day that Sanctions come off Iran, and they become a productive and prosperous nation again".
However, the president said he made a decision to call off the mission after he learned 150 Iranians would die as a result of the strike.
Trump spoke to reporters as he prepared to depart Washington for the presidential retreat Camp David in Maryland, where he said he would be deliberating on Iran. "10 minutes before the strike I stopped it, not proportionate to shooting down an unmanned drone", Trump tweeted on Friday.
"Everybody was saying I'm a warmonger and now they say I'm a dove", he told reporters outside the White House.
The worldwide agreement meant to limit Iran's nuclear program in exchange for relief from earlier sanctions.
Moreover, a war on Iran would inevitably escalate the USA confrontation with China, which can not cede to U.S. imperialism a stranglehold over the oil resources of the Middle East that sustain its economy, and which sees Iran as a strategic link in its One Belt, One Road strategy to deepen the integration of Eurasia. He later said Iran will be hit with unspecified new sanctions on Monday.
Foreign Office minister Andrew Murrison will call for "urgent de-escalation" of flared tensions between the USA and Iran when he holds talks with the Tehran government on Sunday.
But worries about a confrontation between Iran and the United States have mounted despite Mr Trump saying he has no appetite for war.
The IRGC said on Thursday that a U.S. spy drone that violated the Iranian territorial airspace in the early hours of the day was shot down by the IRGC Aerospace Force's air defense unit near the Kooh-e-Mobarak region in the southern province of Hormozgan. Iran has denied involvement.
The president's softer tone Saturday marked a stark contrast to the anti-Iran rhetoric he employed throughout the presidential campaign and presidency, including his use of punishing economic sanctions in an attempt to pressure Iran to give up its quest to build nuclear weapons.
Trump also stressed for multiple times that Washington would not allow Tehran to be armed with a nuclear weapon. "I want people on both sides", he said.
Iran was practicing high-stakes brinkmanship when it shot down a U.S. spy drone on Thursday over the waters of the Strait of Hormuz.
Since shelving the strike, Trump has appeared to be more focused on continuing to squeeze Iran financially through sanctions.
But a Pentagon spokeswoman, Commander Rebecca Rebarich, said on Saturday: "We stand by where we said the aircraft was operating in global airspace". It has also accused European countries of failing to live up to their promises of protecting Iran's economy from United States sanctions.
"We were cocked & loaded to retaliate last night", he said.
General Amir Ali Hajizadeh, the head of the IRGC's aviation division, told Iranian state TV that Iran refrained from shooting down a U.S. Navy Boeing P-8 Poseidon plane with 35 people on board that he said was accompanying the downed drone.