President Trump blasted former Secretary of State John Kerry for meeting with foreign diplomats after he left the State Department.

“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. He told them to wait out the Trump Administration! Was he registered under the Foreign Agents Registration Act? BAD!” Trump tweeted Thursday night.

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. He told them to wait out the Trump Administration! Was he registered under the Foreign Agents Registration Act? BAD!

— Donald J. Trump (@realDonaldTrump) September 13, 2018

The Foreign Agents Registration Act requires agents representing the interests of foreign powers to disclose their relationships with international governments and their related activities and finances.

Kerry admitted Wednesday on Fox News that he met with European and Iranian diplomats but maintained that no negotiations were aimed at undermining the Trump administration’s policies.

“We have conversations with people about the state of affairs in the world in order to understand them. We don’t negotiate, we’re not involved in interfering with policy,” he said.

Kerry was heavily involved in crafting the nuclear agreement between Iran, the U.S. and other major world powers. He denies that his discussions focused on one of the Obama administration’s signature foreign policy achievements.

“It’s not Iran deal-specific, it’s with respect to trade, it’s with respect to NATO,” he said.

A United Nations watchdog certified in August that Iran was complying with the nuclear deal, but the Iranian government has opened the door to potentially rebuilding its stockpile of raw materials needed to create nuclear weapons.

Trump has credited the reimplemented sanctions that accompanied America’s withdrawal from the pact with the pressure the Iranian economy is currently facing and has said he’s open to meeting with Iranian officials regarding a revised nuclear deal.

“Iran, and it’s economy, is going very bad, and fast! I will meet, or not meet, it doesn’t matter – it is up to them!” he tweeted in August.

Iran, and it’s economy, is going very bad, and fast! I will meet, or not meet, it doesn’t matter – it is up to them!

— Donald J. Trump (@realDonaldTrump) August 4, 2018

Iran’s Supreme Leader Ayatollah Ali Khamenei poured cold water on the prospect, responding, “With current brazen U.S. officials—who have unsheathed their swords against Iranians—what negotiations can we have? Thus no negotiations with any U.S. official at any level will be held.”

Negotiations with former U.S. officials, who at least saved some face, bore such results! With current brazen U.S. officials—who have unsheathed their swords against Iranians—what negotiations can we have? Thus no negotiations with any U.S. official at any level will be held.