Secretary of State John F. Kerry answers questions in Boston. (Faith Ninivaggi/Reuters)

Secretary of State John F. Kerry on Tuesday defended the decision not to make the release of three Americans imprisoned in Iran a condition for a nuclear agreement with Iran.

Kerry, speaking at a news conference in Boston, said the State Department had raised the issue of the three Americans, including Washington Post correspondent Jason Rezaian, on the sidelines at every meeting during months of negotiations. But he said negotiators did not want to make their fate an integral part of the talks — which he characterized as a decision “not to hold a nuclear agreement hostage to hostages.”

“And in our judgment, it was the right thing to do because it could have complicated both significantly and perhaps have resulted in nothing happening on either,” he said. “So I think it was the right strategy to pursue.”

Many members of Congress have criticized the administration for reaching a historic agreement on Iran’s nuclear program without guaranteeing the release of three Americans citizens who have been convicted on what the State Department considers spurious charges. The deal, to lift sanctions if Iran curtails its nuclear program, was reached in July.

Rezaian was accused of espionage and other charges, and over the weekend the court's judiciary spokesman told reporters Rezaian had been convicted, though it is not clear when, on what charges or what sentence has been imposed.

Saeed Abedini, a pastor from Boise, Idaho, also is imprisoned in Iran after being found guilty of endangering national security by holding private religious services in home churches. Amir Hekmati, a former Marine from Flint, Mich., was accused of being a spy when he was arrested on a visit to Iran to see his grandmother, and has spent four years in an Iranian prison. In addition, the United States is seeking information on the whereabouts of Robert Levinson, who disappeared in Iran in 2007.

Kerry bemoaned the fact that there is still no official confirmation of the verdict against Rezaian, just Iranian media reports of what the judiciary spokesman said. He said the State Department is continuing a “dialogue” with Iran regarding the Americans, “and we will until they come home.”

Kerry also urged Iran to drop all charges against the three who are in prison and free them immediately.

"We call on the government of Iran – whether they’ve had a conviction with a sentence or no sentence, whatever the status is — we call on the government of Iran to release these individuals, to drop all the charges, and to see them reunited with their families here in the United States," he said.

“And I can assure you when they do return and people gain full knowledge on the efforts that have been made, nobody will see anything except an extraordinary, continued, highly focused, intensive effort to secure their release.”