Jason Rezaian
Jason RezaianReuters

Jason Rezaian, the Washington Post reporter who was recently released from an Iranian prison after 18 months as part of a prisoner swap with the United States, on Thursday made his first public appearance since his release, Reuters reported.

Rezaian thanked U.S. Secretary of State John Kerry for negotiating his release, according to the report during his appearance at a ceremony for the opening of the Washington Post's new offices in Washington, D.C.

A joint American-Iranian citizen, Rezaian was arrested in July 2014 and accused of spying.

Following a closed-door trial, Iran announced in late November that Rezaian was sentenced to a prison term before he was freed in the prison swap which coincided with the implementation of the nuclear deal between Iran and the West.

Rezaian received a standing ovation from foreign dignitaries, journalists and family members as he arrived at Thursday’s ceremony.

In brief but emotional remarks, he thanked the Washington Post leadership, U.S. officials, and his family for advocating on his behalf.

"For much of the 18 months I was in prison, my Iranian interrogators told me that the Washington Post did not exist, that no one knew my plight, and that the United States government would not lift a finger for my release," Rezaian said, according to Reuters. "Today I'm here in this room with the very people who helped prove the Iranians wrong in so many ways."

He highlighted the efforts of Kerry and Brett McGurk, a State Department envoy who conducted secret negotiations with Iran to secure the prisoner deal.

Kerry told attendees Rezaian's detention weighed heavily on U.S. officials.

"This gnawed at us, because we sensed the wrongfulness and we knew that Jason and others were living the consequences," he said, according to Reuters.

The Secretary of State also stressed that officials are continuing to try to find out what happened to Robert Levinson, a former FBI agent who went missing in Iran eight years ago and was not part of the swap.

Levinson’s family said in a statement following the deal that they were "devastated" that Levinson had been "left behind."

White House Press Secretary Josh Earnest recently claimed that Washington has “reason to believe” that Levinson is “no longer in Iran” and had mentioned that belief “several years ago.”