Pompeo said he would "leave the legal determinations to others", but made it crystal clear he strongly disapproved of Kerry's actions.
Later in the day, Kerry was asked by Fox News' Dana Perino if he told the Iranians to simply hold out until 2020, when Trump could be voted out of office.
"You can't find precedent for this in US history, and Secretary Kerry ought not to engage in that kind of behaviour", an agitated Pompeo told reporters at the State Department.
Manisha Singh, the assistant Secretary of State for economic affairs, told the House Foreign Affairs Committee today that such meetings would be "very inappropriate".
He added, "Actively undermining USA policy, as a former secretary of state, is literally unheard of". Secretary (Henry) Kissinger has done it for decades with Russian Federation and China.
Kerry, busy plugging a new book, admitted this week that he's met "three or four times" with Zarif since leaving office.
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.
"Unfortunately, we have a president, literally, for whom the truth, the whole truth and nothing but the truth is three different things, and you don't even know what they are", said Kerry. Was he registered under the Foreign Agents Registration Act? BAD!
The Commander-in-Chief ripped Kerry's "illegal meetings" with the "hostile Iranian regime" on social media, saying the former diplomat was aiming to "undercut our great work" in cracking down on the Islamic Republic.
Pompeo, the current secretary of state, followed up on Trump's criticism at a briefing, calling the meetings "unseemly", "unprecedented" and "beyond inappropriate".
As of this writing, Kerry, who is now promoting his new book "Every Day is Extra", has not responded to Trump's or Pompeo's broadsides.
Kerry played a crucial role in crafting the Obama-era Iran nuclear agreement.
"I wasn't in the meeting, but I am reasonably confident that he was not there in support of US policy with respect to the Islamic Republic of Iran, who this week fired Katyusha rockets toward the United States embassy in Baghdad and took action against our consulate in Basra", Pompeo continued.
"Mr President, you should be more anxious about Paul Manafort meeting with Robert Mueller than me meeting with Iran's FM", Mr Kerry said on Twitter shortly after Mr Pompeo's remarks, referring to Mr Trump's former campaign chairman who yesterday agreed to co-operate with federal investigators into Russian meddling in the 2016 United States election. I've also seen reports that he is apparently providing, according to reports, advice to the Iranian government. "The devil's always in the details", Rosenstein told the AP. Met Zarif again in NY in April.
In this January 15, 2017 file photo, U.S Secretary of State John Kerry speaks with the media after attending the Mideast peace conference in Paris. "Stay away from negotiations John, you are hurting your country!" he said on May 8. "He was the one that created this MESS in the first place!" A third is reported to have occurred at the United Nations headquarters, which is not technically on US soil. He has also accused the Trump administration of pursuing a policy of regime change in Iran.