Iran live updates: Iran targets US forces, Kuwait airport amid ceasefire

Secretary of State Marco Rubio said that although the new Supreme Leader of Iran Ayatollah Mojtaba Khamenei has not been seen or heard from publicly, "there are indications out there that he is increasingly engaging at some level” in negotiations with the U.S.

Rubio added that all of his communications have been through writing and intermediaries.

Rubio said Iranian negotiators would often need “three to five days to get a response” from Iranian leadership.

"Now, some of it is logistical,” Rubio said. ‘They’re operating--probably using couriers and things of this nature. Part of it is internal fissures on exactly what they should agree to or not agree to.”

Rubio said there were also "communications issues within the regime as well,” saying that many tactical decisions were being made at the commander-level.

“You ultimately are negotiating with people who then have to negotiate within their own system to see what they're allowed to give and what they're allowed to agree to,” he said.

Secretary of State Marco Rubio provided more information on what the administration wants Iran to commit to in an initial agreement before moving into detailed nuclear negotiations while testifying before Congress on Tuesday.

“They have to commit to very specific negotiations on the disposition of the highly enriched uranium that still is buried deep in a mountain somewhere,” he said. “They have to agree on negotiating severe and long-term limitations and/or cancelation of enrichment activity in their country.”

Rubio said the details on these matters would need to be worked out in future talks, but to enter that phase Iran would “have to commit to their willingness to do that.”

"For example, they have to commit to say 'we will dispose of the enriched uranium.' And the question now is what are the mechanisms by which we do so? That can be negotiated,” he said.

A senior Hezbollah leader said the group agreed to a "genuine and comprehensive" ceasefire but will respond to bombings of southern Lebanon by targeting locations deeper than the northern Israeli settlements.

Testifying before the Senate Foreign Affairs Committee, Secretary of State Marco Rubio repeated the claim that Iran desired to build a nuclear weapon and was on the cusp of developing a shield of conventional arms that would allow it to pursue that goal.

"The president chose to act to deny them that point of immunity," Rubio said.

On the odds of an agreement to end the war, Rubio commented on the difficulties of the indirect negotiations, but still asserted a deal was possible.

“There is the prospect before us, which could happen today, it could happen tomorrow, it could happen next week,” he said.

Rubio said Iran had agreed to hold negotiations on its nuclear program.

"That is not a guarantee that ultimately it will lead to a deal that's acceptable to the Senate or acceptable to the American people, but we'll be able to engage them in a process to truly test the proposition of how far they're willing to go,” he said.