(CNN) -- President Donald Trump took to Twitter on Monday to condemn former Secretary of State John Kerry for engaging in "shadow diplomacy" to try to preserve the Iran nuclear deal by holding meetings and speaking with major players, who, like Kerry, do not want Trump to withdraw the US from the agreement.
Kerry met with Iranian Foreign Minister Javad Zarif at the United Nations in New York two weeks ago, their second meeting in about two months, to discuss ways of keeping the deal limiting Iran's nuclear weapons program intact, according to two sources familiar with the interactions.
The former secretary of state also met last month with German President Frank-Walter Steinmeier, separately sat down with French President Emmanuel Macron and spoke on the phone with European Union foreign policy chief Federica Mogherini, the sources told CNN.
The Boston Globe was first to report Kerry's meetings with Zarif, Steinmeier and Mogherini.
Trump slammed Kerry's reported engagement on Monday.
"The United States does not need John Kerry's possibly illegal Shadow Diplomacy on the very badly negotiated Iran Deal. He was the one that created this MESS in the first place!" Trump tweeted.
But a Kerry spokesman pushed back against Trump's remarks in a statement on Monday.
"I think every American would want every voice possible urging Iran to remain in compliance with the nuclear agreement that prevented a war. Secretary Kerry stays in touch with his former counterparts around the world just like every previous Secretary of State," said the spokesman in a written statement. "Like America's closest allies, he believes it is important that the nuclear agreement, which took the world years to negotiate, remain effective as countries focus on stability in the region."
Kerry has also quietly lobbied members of Congress, including House Speaker Paul Ryan, placing dozens of phone calls in recent weeks.
During his Friday speech to the National Rifle Association, Trump attacked Kerry for his initial role in negotiating the Iran deal, which Trump called "horrible."
"And we have the former administration as represented by John Kerry, not the best negotiator we've ever seen," Trump said. "He never walked away from the table, except to be in that bicycle race where he fell and broke his leg."
The Trump administration faces a May 12 deadline to decide whether to continue waiving sanctions on Iran that were lifted under the 2015 Iran deal, formally known as the Joint Comprehensive Plan of Action.
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