Sen. Tom Cotton and Iranian Foreign Minister Javad Zarif have entered another round of one-on-one Twitter sparring, which  is apparently their new preferred method of conducting diplomacy.

Cotton’s opening shots came after Zarif spoke at New York University Wednesday, discussing his interpretation of the process by which American sanctions against Iran will be lifted, if a final nuclear agreement is reached by June 30. The Iranian government’s staunch position has been that all nuclear-related sanctions will be lifted as soon as a deal is reached, while the U.S. insists that sanctions relief will be “phased” as Iran shows signs of compliance. (RELATED: One Unanswered Question Remains For Obama’s Iran Deal)

In his remarks, Zarif referred to Cotton by name, saying that the sanctions regime would be suspended if a deal was reached, “whether Sen. Cotton likes it or not.”

In response, Cotton noted that he’d heard Zarif “called me out” at NYU. Referring to their previous spat over Cotton’s open letter to Supreme Leader Ayatollah Khamenei, in which he threatened on Constitutional principles to veto any final deal with Iran, he invited Zarif to Washington to have a debate about the Constitution. (RELATED: Iranian Official Greeted In New York With ‘Hanging Party’ Prank)

Hey @JZarif, I hear you called me out today. If you’re so confident, let’s debate the Constitution. 1/4

— Tom Cotton (@SenTomCotton) April 29, 2015

Here’s offer: meet in DC, @JZarif, time of your choosing to debate Iran’s record of tyranny, treachery, & terror. 2/4

— Tom Cotton (@SenTomCotton) April 29, 2015

He went on to point out Zarif’s personal history, saying he “hid” in the U.S., obtaining four American university degrees while Iranian “peasants & kids” died in the Iran-Iraq war. On these grounds, he suggested, Zarif might be too “cowardly” to accept the invitation.

I understand if you decline @JZarif after all, in your 20s, you hid in US during Iran-Iraq war while peasants & kids were marched to die 3/4

— Tom Cotton (@SenTomCotton) April 29, 2015

Not badge of courage @JZarif, to hide in US while your country fought war to survive-but shows cowardly character still on display today 4/4

— Tom Cotton (@SenTomCotton) April 29, 2015

The exchange came less than a day after Cotton announced the birth of his son Gabriel, prompting one observer to joke that “22 hours is enough parenting for now.”

Yup 22 hours is enough parenting for now, time to go provoke a foreign minister pic.twitter.com/6fxB5Wcfa2

— Kelsey D. Atherton (@AthertonKD) April 29, 2015

Zarif issued his reply on Thursday, suggesting that the key to a healthy working relationship between Iran and the U.S. was “serious diplomacy,” not a “personal smear.” He went on to congratulate Cotton on the birth of his son, hoping that the senator’s family could “enjoy him in peace.”

Serious diplomacy, not macho personal smear, is what we need. Congrats on Ur new born. May U and Ur family enjoy him in peace .@SenTomCotton

— Javad Zarif (@JZarif) April 30, 2015

Zarif has cultivated a reputation as the smooth, affable face of Iranian foreign policy abroad, at a time when the country is making increasingly bold moves in the region and attempting to secure a lasting agreement to develop its nuclear energy program. Cotton alluded to one such move, the capture of a private cargo ship with commercial ties to the U.S., in a statement issued on his website. (RELATED: Iranian Media Claims Capture Of US Ship, Pentagon Denies)

The Senate this week is debating amendments to a bill that would require Congressional approval on any final deal between Iran and the U.S. The amendments include a requirement for the U.S. government to certify that Iran does not sponsor international terrorism, and a proposal by Sen. Marco Rubio to make Iranian recognition of Israel a precondition for a final deal.

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