Former Secretary of State Mike Pompeo on Tuesday said he was "disheartened" but not surprised by allegations that his predecessor John Kerry had informed a top Iranian official of Israeli operations in Syria -- and said Kerry needs to explain what he did or did not say.

"I was unsurprised," Pompeo told Fox News Digital in an interview on Tuesday. "But it reminded me that every leader has a special responsibility to defend their oath to the Constitution, and when I heard Foreign Minister [Javad] Zarif talk about the fact he learned about Israeli operations in Syria from an American former secretary of state, it was truly disheartening."

IRAN'S FOREIGN MINISTER SAYS JOHN KERRY TOLD HIM ABOUT ISRAELI COVERT OPERATIONS IN SYRIA 

Zarif said in leaked audio obtained by The New York Times and other outlets, that he was astonished when Kerry revealed that Israel had attacked Iranian targets in Syria more than 200 times. It is unclear when the alleged conversation took place.

Kerry, who serves as President Biden's National Security Council special climate envoy, has denied telling Iran information about Israeli military operations, calling the allegations "unequivocally false."

But Republican critics have noted that Kerry has long faced accusations of forming back channels with the Iranians -- even as the Trump administration was pursuing a "maximum pressure" policy against Tehran and withdrawing from the Kerry-backed Iran deal.

"We knew Secretary Kerry was out talking to the Iranians," Pompeo said on Fox News Channel's "The Story." "We knew that the administration, the previous administration, was actively telling the Iranians, look, this maximum pressure campaign that the Trump administration has put in place, you can wait it out." 

The Trump administration withdrew from the Iran deal and imposed waves of sanctions on Tehran. The Biden administration has indicated it wants to reenter the accord and has stopped pursuing a Trump-era effort to reimpose United Nations sanctions on the regime.

The State Department has pushed back on the controversy, saying the strikes were in the public realm at the time.

"I would just make the broad point that if you go back and look at press reporting from the time, this certainly was not secret," a State Department spokesman said Monday, according to the Times. "And governments that were involved were speaking to this publicly, on the record."

While it is not clear when the conversation took place, Pompeo said the comments would never be appropriate, considering Iran is a key adversary. 

"The timeline is significant in terms of what risk it might have presented to Israeli operations or operations conducted by our allies and friends, but in the bigger picture, there's no timeline for when such commentary would be appropriate," he told Fox News Digital. "It certainly appears from Foreign Minister Zarif’s words that the timeline provided him the information prior to the time the Iranians were capable, or the foreign ministry was capable of learning about those actions."

CALLS FOR JOHN KERRY TO BE INVESTIGATED FOR WHAT HE TOLD IRAN

A number of Republicans have called for investigations, and even for Kerry to step down. Pompeo said that it was important for Kerry to at least explain what he said, and when. He noted that Kerry has previously said he and Zarif had met only a few times -- but not how many times they spoke.

"He was very crisp in his response to how many meetings they had, he didn't say how often or frequently they were speaking by phone or text message or email," he said. "It would be important to understand the scope of communications."

CLICK HERE TO GET THE FOX NEWS APP

Pompeo also noted the allies are watching the controversy to see if the U.S. can be trusted with important information.

"They're watching to see whether they can trust the United States with information that they provide us," he said on "The Story." "The American people need to know what took place. And I hope the secretary will come forward and explain precisely what it was they were talking about, how many times he spoke to them, that he'll share information he may have on his phones, all the things that would help us understand what it was Secretary Kerry was talking to Foreign Minister Zarif about."