"I think there are indications out there that he is increasingly engaging at some level," Rubio told the Senate Foreign Relations Committee.

Mojtaba Khamenei, 56, succeeded his father Ali Khamenei, who was killed in the first wave of US-Israeli strikes that launched the war on February 28.

Rubio was testifying in front of the Senate panel as talks on ending the three-month-old war that has engulfed the Middle East and triggered a global energy crisis have stalled.

Rubio expressed hope for a deal with Iran, while insisting that Tehran must severely limit its nuclear program in order to see sanctions lifted.

"There is the prospect before us, which could happen today, it could happen tomorrow, it could happen next week," Rubio said.

Rubio said that Tehran must agree to reopen the Strait of Hormuz, a key shipping channel for Gulf oil and gas.

"They have to announce very clearly 'The straits are now open, we're not charging a toll'." We will help remove the mines that they put in there, and they will not fire on ships."

Additionally, he said: "They have to agree on negotiating severe and long-term limitations and/or cancellation of enrichment activity."

Rubio continued: "Iran is being sanctioned because they've highly enriched uranium, Iran is being sanctioned because of their nuclear activities, if they agree to give up those things, there will be sanctions relief."