Iran’s foreign minister on Thursday fired back at Sen. Tom Cotton’s series of tweets calling for a debate on the U.S. Constitution, a day after the freshman Arkansas Republican proposed that the two meet in Washington to debate “Iran’s record of tyranny, treachery and terror.”

Mohammad Javad Zarif responded, congratulating Cotton on the birth on Monday of his son, Gabriel.

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

Cotton’s tweets followed remarks by Zarif at New York University on Wednesday, in which he said United Nations sanctions would be lifted if there is a nuclear deal, “whether Sen. Cotton likes it or not.”