As the world's leaders meet at the U.N. General Assembly, Secretary of State John Kerry sat down with Greta Van Susteren for a must-see interview.

During the sit-down, Van Susteren asked Kerry about the Americans being held in Iran, including a Christian pastor, a Washington Post reporter and a Marine.

She asked whether a prisoner swap, mentioned recently by the Iranian president, may happen soon. 

Kerry declined to comment on whether a swap might occur, but said he remains "fixated" on brokering the release of the Americans.

"I’m not going to discuss what we might or might not do. I will discuss that we are in every conversation now talking about this issue and it’s my hope that over the course of the next days, weeks but as short as possible, I hope our citizens will come home and we’re continuing to focus on it," said Kerry.

Watch a preview clip below and see Greta's full interview with Secretary Kerry, tonight at 7p ET on "On the Record."