“We’ve achieved this historic progress through diplomacy," the president said, "without resorting to another war in the Middle East."

Jacquelyn Martin / AP

President Obama said Sunday that the formal implementation of the Iranian nuclear deal, combined with a successfully negotiated prisoner exchange with Tehran, shows what is possible through "strong American diplomacy." Fending off attacks from his critics that he has not been strong enough with Iran, Obama highlighted the weekend's progress with Tehran as part of an impassioned defense of his administration's emphasis on diplomacy following decades of minimal communication between the two nations. "We've achieved this historic progress through diplomacy, without resorting to another war in the Middle East," the president said. His speech at the White House came a day after the U.S. formally lifted its sanctions on Iran in connection with the country's nuclear program. The move was taken after the U.N. nuclear watchdog verified that Iran had lived up to its end of a deal struck with six world powers in July and dismantled large swathes of its nuclear sector. The president said that the agreement has ensured Iran won't have enough material to create even one nuclear weapon, and vowed the U.S. will make sure the Iranians don't cheat on the deal. "We have now cut off every single path that Iran could have used to build a bomb," he said. "The region, the United States, and the world will be more secure." There are sanctions remaining on Iran, though, including new sanctions on its ballistic missile program announced by the Treasury Department on Sunday.

Vahid Salemi / AP Jason Rezaian.

Also on Saturday, the U.S. and Iran each announced they were releasing prisoners as part of an exchange agreement. The Americans released in the deal were Jason Rezaian, a Washington Post reporter; former Marine Amir Hekmati; Saeed Abedini, a pastor; and Nosratollah Khosravi-Roodsari. A fifth American, Matthew Trevithick, was also released separately. The U.S. offered clemency to seven Iranians in return for the prisoners. Many Republican contenders for the president were critical of the swap, saying the U.S. shouldn't have returned people who had been through the American justice system for detainees facing trumped up charges in Iran. Obama, though, said he had spent much time with the families of the released prisoners, and was thrilled to welcome them back to the U.S. "Today, we're united in welcoming home sons and husbands and brothers who in lonely prison cells have endured an absolute nightmare," the president said. A senior administration official who later briefed reporters on the condition of anonymity said negotiations to secure the prisoners' release began some 14 months ago on the sidelines of the nuclear discussions. The discussions were mostly held in Switzerland in secrecy, the official said. Obama said the U.S. was still committed to searching for Robert Levinson, a former FBI agent who disappeared while in Iran in 2007. The senior administration official said the U.S. and Iran would "continue a dialogue through multiple channels" to facilitate the return of missing people, including Levinson. Highlighting the brief detention and release of 10 U.S. Navy sailors who strayed into Iranian waters last week, Obama said the quick resolution to the matter was further evidence of a better relationship with Iran than in previous years. "That could have sparked a major international incident," he said. "Instead, we worked directly with the Iranian government and secured the release of our sailors in 24 hours."

Jacquelyn Martin / AP Obama speaking Sunday.