A 15-minute walk Iranian Foreign Minister Mohammad Javad Zarif took with Secretary of State John Kerry along the banks of the Rhone River in Geneva last month, during a break in negotiations over Iran’s nuclear program, has resulted in a major brouhaha. Iranian hard-liners, who continue to look for ways to embarrass the government of President Hasan Rouhani and even to derail the nuclear talks, pounced on this stroll, denounced Mr. Zarif for failing to uphold Iran’s honor and for hobnobbing with a representative of the Great Satan.

Friday prayer leaders in major cities, who get their weekly talking points from a central office in Tehran, criticized the foreign minister. A prayer leader in Tehran, addressing unnamed government officials, noted: “You are talking to wild animals who have no mercy on the powerful or the weak and insult the most sacred prophet. … They openly support the Zionists and then we, publicly, should go and take a stroll with them?”

The commander of the para-military Basij forces, Mohammad Reza Naqdi, called Mr. Zarif’s “intimacy with the enemy of humanity” wrong-headed and described the walk as equivalent to “trampling on the blood of martyrs.”

In parliament, several took to the floor to criticize Mr. Zarif. “What does it mean to take a walk with the foreign minister of a country that, in the history of our nation, has only committed crimes and treason?” asked one influential parliamentarian. Nearly two dozen deputies signed a petition to summon the foreign minister for what they described as intensive questioning. (The summons has yet to be officially issued.)

Mr. Zarif has weathered much of this with aplomb. After returning from Geneva last month, he took the unusual step of riding the Tehran metro, chatting with ordinary Iranians on their way to work and explaining his stroll with Mr. Kerry as a break from intensive negotiations.

The editor of the hard-line newspaper Kayhan, Hossein Shariatmadari, who is close to Supreme Leader Ayatollah Ali Khameini, initiated the attacks on Mr. Zarif with a signed editorial in which he criticized the stroll and took Mr. Zarif to task for traveling to Paris to meet with French Foreign Minister Laurent Fabius the same week people took to the streets in France to denounce the massacre of Charlie Hebdo journalists over cartoons seen as insulting to the prophet of Islam.

Last week, Mr. Shariatmadari went further. He compared Mr. Zarif to a soccer player “who repeatedly shoots goals through his own [team’s] goalposts” and called on “the coach”–meaning President Rouhani–to sub out the offending player or take responsibility for the errors himself.

This editorial came in response to remarks by President Rouhani, who at a recent university event accused critics of his negotiating team of “cheering for opposing side” and nit-picking. The president, tongue in cheek, compared the criticism of Mr. Zarif to objecting because “a diplomat walked fast, or his coat was askew.”

This is more than nit-picking. It is striking that while the supreme leader has, in a manner, continued to support the Iranian negotiating team, he has also permitted this barrage of criticism of the president, his foreign minister and Iran’s negotiators at a sensitive juncture in the nuclear negotiations.

The opinions expressed here are solely those of the author.

This article was originally published in The Wall Street Journal's Washington Wire.