President Trump took fresh aim Thursday evening at former secretary of state John F. Kerry, accusing him of engaging in “illegal” meetings with an Iranian official.

In a radio interview this week to promote a new book, Kerry said he had met with Iranian Foreign Minister Mohammad Javad Zarif “three or four times” since leaving office and that their discussions included the nuclear deal that Trump has since scrapped.

Kerry said such meetings are appropriate, later explaining during a television interview on Fox News that “every secretary of state, former secretary of state, continues to meet with foreign leaders, goes to security conferences, goes around the world.”

In a Thursday night tweet, Trump took a different view, echoing criticism from conservative pundits from recent days.

“John Kerry had illegal meetings with the very hostile Iranian Regime, which can only serve to undercut our great work to the detriment of the American people,” Trump said. “He told them to wait out the Trump Administration!”

The latter assertion was a reference to a question Kerry fielded in his Fox News appearance about whether he has told Iranians to “wait out” Trump until there is a new president. Kerry did not answer directly.

“I think everybody in the world is talking about waiting out President Trump,” said Kerry, a former senator from Massachusetts who was the 2004 Democratic presidential nominee.

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In his tweet, Trump asked whether Kerry had complied with the Foreign Agents Registration Act. That statute requires those who represent the interests of foreign governments in a “political or quasi-political capacity” to disclose those relationships and details about their activities.

It was not clear from Trump’s tweet why he thought Kerry would need to register.

Others who have criticized Kerry have suggested that he might have violated the Logan Act, which prohibits private citizens from negotiating on behalf of the U.S. government without authorization.

There are only two known instances in which individuals have been indicted on a charge of violating the Logan Act — most recently in 1853 — and neither indictment resulted in conviction, according to legal experts.

When asked Friday about Trump’s claim that Kerry’s contacts were “illegal,” Secretary of State Mike Pompeo said he would “leave the legal determination to others” but called Kerry’s actions “unseemly and unprecedented.” 

 “A former secretary of state engaged with the world’s largest state sponsor of terror, and according to him, he was talking to them, he was telling them to wait out this administration,” Pompeo said at a news conference at the State Department. “You can’t find precedent for this in U.S. history.” 

A spokesman for Kerry hit back at Pompeo, saying that the former diplomat’s contacts with Iranian officials over the past several months were clearly above board. 

“There’s nothing unusual, let alone unseemly or inappropriate, about former diplomats meeting with foreign counterparts,” spokesman Matt Summers said in a statement. “What is unseemly and unprecedented is for the podium of the State Department to be hijacked for political theatrics.”

Trump also targeted Kerry in May after a Boston Globe report about his meetings with officials involved in the Iran nuclear deal, which he helped craft while secretary of state under President Barack Obama.

In a tweet at that time, Trump accused Kerry of “possibly illegal Shadow Diplomacy” and criticized him for having negotiated “very badly.”

“He was the one that created this MESS in the first place!” Trump wrote at the time. 

 In recent years, both U.S. political parties have accused each other of undermining a sitting U.S. president on Iran policy. 

 In 2015, while the Obama administration was seeking a nuclear deal with Iran, 47 Republican senators led by Sen. Tom Cotton (R-Ark.) wrote a letter to Iran’s supreme leader, Ayatollah Khomenei, warning that Congress could alter the deal after Obama left office. 

Democrats at the time accused Republicans of undermining the president’s foreign policy.