Pompeo stopped short of calling Kerry's meetings a violation of FARA, saying he would "leave the legal determinations to others".
"You can't find precedent for this in U.S. history, and Secretary Kerry ought not to engage in that kind of behavior", an agitated Pompeo told reporters at the state department.
"He is the first president that I know of who spends more time reading his Twitter "likes" than his briefing books or the constitution of the United States", Kerry told Maher.
He added: "Actively undermining US policy as a former secretary of state is literally unheard of".
The tweet was an apparent reference to Kerry admitting on Hugh Hewitt's radio show on Wednesday to meeting with Iranian officials, specifically Foreign Minister Javad Zarif, "three or four times" at gatherings of world leaders, such as the World Economic Forum.
The Foreign Agents Registration Act (FARA) is a disclosure statement that requires a person acting as an agent of a foreign principal in a political or quasi-political capacity to make public disclosure of their relationship with the foreign principal.
Pomepo's criticizing of the former MA senator followed a scolding tweet from US President Donald Trump, who accused Kerry of breaking American law by meeting with the Iranians, including with Foreign Minister Mohammad Javad Zarif.
In his tweet, Trump asked whether Kerry had complied with the Foreign Agents Registration Act. "What is unseemly and unprecedented is for the podium of the State Department to be hijacked for political theatrics", he said.
Trump withdrew the United States from the nuclear deal with Iran in May and his administration has pushed a hard line against Tehran as it moves to reimpose sanctions that were lifted after the deal.
"I am confident that they met with their troika [Iranian] counterparts", he said. I've also seen reports that he is apparently providing, according to reports, advice to the Iranian government.
Such meetings, between a private USA citizen and foreign official, are not against the law and not necessarily inappropriate or a violation of federal regulations, but Trump and his allies say they are evidence that former Obama administration officials are trying to subvert Trump's policy.
"The devil's always in the details", Rosenstein said. The meetings came while Rex Tillerson was secretary of state and before Trump's withdrawal from the JCPOA in May.
Kerry told Hewitt that he was not coaching the Iranians on how to deal with the Trump administration.
Sure, Kerry now says he's merely "trying to elicit what Iran might be willing to do in order to change the dynamic in the Middle East for the better".