Kerry says release of US sailors 'testament' to Iran diplomacy, nuke deal going forward

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Hours after Iran released U.S. sailors from custody, Secretary of State John Kerry and the Obama administration portrayed the incident as a “testament” to the new diplomatic relationship between Washington and Tehran -- while indicating it would have no effect on plans to flip the switch on the Iran nuclear deal in a matter of days.

“I think we can all imagine how a similar situation might have played out three or four years ago,” Kerry said Wednesday, thanking Iranian officials for their cooperation in the tense Persian Gulf incident.

Despite the upbeat message, though, Republican lawmakers pointed to the stand-off in renewing their concerns about the nuclear deal and, specifically, a string of Iranian provocations in recent weeks. And they warned about the implications of freeing up billions of dollars in sanctions relief.

“One hundred billion dollars to the world’s biggest state sponsor of terrorism only emboldens Iran to harm more Americans,” Sen. Mark Kirk, R-Ill., said in a statement.

Sen. David Perdue, R-Ga., said: “As we near President Obama’s implementation of the Iran nuclear deal, which could be as soon as this weekend, Iran continues to engage in dangerous saber-rattling. We need to see more from our Commander-in-Chief than empty rhetoric when it comes to Iran.”

In the House, lawmakers initially approved a bill Wednesday to intensify sanctions on Iran, in the face of a presidential veto threat -- though House leaders vacated the vote, after dozens of lawmakers missed it, and plan to reschedule.

But Kerry insisted that the nuclear deal implementation will take place soon.

“Implementation Day – which is the day on which Iran proves it has sufficiently downsized its nuclear program and can begin to receive sanctions relief – is going to take place very soon, likely within the next coming days,” Kerry said.

Other officials told The Associated Press an announcement could come as soon as Friday.

Such an announcement would mean the U.N. atomic energy watchdog has found Iran to have met its obligations to curb its nuclear program. It would then require the U.S. and other nations to immediately suspend many sanctions they have imposed on the Islamic republic.

Despite this movement, questions remain over what exactly transpired in the Persian Gulf, hours before President Obama delivered his State of the Union address.

Iran's Revolutionary Guard had detained 10 U.S. Navy sailors after two small Riverine boats crossed into Iranian territorial waters – and released them Wednesday morning.

A U.S. official told Fox News that the sailors were initially taken to the guided-missile cruiser USS Anzio before flying to the aircraft carrier USS Harry S. Truman for additional debriefing.

A Pentagon statement said the Navy would "investigate the circumstances that led to the Sailors' presence in Iran."

Officials are still uncertain of how Iranian forces managed to commandeer the two boats. The U.S. official told Fox News that a mechanical problem on at least one of the boats could not be ruled out, but could not explain how both boats were able to get underway in such a short time if one did have a propulsion issue, which would have caused it to stop running and drift into Iranian territorial waters.

It was not immediately clear whether the U.S. and Iran had made a specific arrangement to secure the sailors’ release.

Fox News' Jennifer Griffin and Lucas Tomlinson and The Associated Press contributed to this report.