Last Updated, 10:24 p.m. | Iran’s new foreign minister, the veteran diplomat Mohammad Javad Zarif, formally took charge of the country’s nuclear negotiations on Thursday, but still managed to find time to reach out to the West through a more informal channel — his new Twitter account.

Plunging headfirst into public diplomacy, Mr. Zarif chose to open his dialogue with fellow users of the social network by extending greetings for the Jewish New Year, Rosh Hashanah.

Later in the day, when his tweet was challenged by one skeptical reader — Representative Nancy Pelosi’s daughter Christine — the American-educated diplomat, who lived in the United States for three decades, made his message that the Ahmadinejad era was over even more explicit, insisting that the nation of Iran had never denied the Holocaust. As a screenshot of the exchange posted online by Ms. Pelosi showed, Mr. Zarif added, “the man who did is now gone,” before subsequently recasting that comment to offer a more charitable reading of stance taken by Iran’s former president, Mahmoud Ahmadinejad.

Thanks. The New Year would be even sweeter if you would end Iran’s Holocaust denial, sir. “@JZarif: Happy Rosh Hashanah” — sfpelosi (@sfpelosi) 5 Sep 13

@sfpelosi Iran never denied it. The man who was perceived to be denying it is now gone. Happy New Year. — Javad Zarif (@JZarif) 5 Sep 13

Mr. Zarif subsequently confirmed in conversations with Christiane Amanpour of CNN and the journalist Robin Wright that the comments posted on the @JZarif account were his own and that he was aware he had engaged in conversation with the daughter of a prominent American politician.

Just spoke with Iranian FM @JZarif – who confirms he IS tweeting and wishes Jews in Iran & around the world a happy new year! — Ditto! — Christiane Amanpour (@camanpour) 5 Sep 13

Just heard from @jzarif, who confirms that he was fully aware that he was having Twitter exchange Nancy Pelosi’s daughter @sfpelosi. Wow! — Robin Wright (@wrightr) 5 Sep 13

Having started with an attempt to undo the damage to Iran’s international reputation caused by the former president’s anti-Semitic rhetoric, Mr. Zarif quickly moved on to the issue of chemical weapons, posting a link to his Facebook page, where he shared thoughts on the “recent abhorrent developments in Syria.”

unequivocal rejection of #chemicalweapons, militarism and impermissible use of force. some thoughts //t.co/7lu9kBtD2r. — Javad Zarif (@JZarif) 5 Sep 13

When a Texan carpenter challenged Mr. Zarif’s message repudiating the use of chemical weapons and militarism — asking, “Does that include nuking Israel?” — Iran’s chief diplomat replied: “We do not have nukes. They do.”

On Facebook, Mr. Zarif suggested that rebel forces in Syria might have used chemical agents and noted that the American government had been less concerned by the use of chemical weapons in the 1980s, when Iraq’s military gassed Iranians.

Any use of chemical weapons must be condemned, regardless of its victims or culprits. This is Iran’s unambiguous position as a victim of chemical warfare. But has it always been the position of those who are now talking about punishing their presumed culprit? How did they react when civilians in Iran and Iraq were victims of independently established massive and systematic use of advanced chemical weapons by their then-friend Saddam Hussein?

Although Mr. Zarif refrained from commenting Thursday on whether President Bashar al-Assad’s forces were guilty of poison gas attacks, he did, as The Washington Post reported, tell an Iranian newspaper earlier in the week, “We believe that the government in Syria has made grave mistakes that have, unfortunately, paved the way for the situation in the country to be abused.”

His Twitter outreach came one day after an account maintained in the name of Iran’s new president, Hassan Rouhani, posted similar warm wishes for the Jewish New Year.

As the sun is about to set here in #Tehran I wish all Jews, especially Iranian Jews, a blessed Rosh Hashanah. //t.co/tmaf84x7UR — Hassan Rouhani (@HassanRouhani) 4 Sep 13

The conservative Iranian news agency Fars quickly posted a comment from an adviser to the president denying that the account was an official one. “Mr. Rouhani does not have a tweeter account,” Fars quoted the adviser, Mohammad Reza Sadeq, as saying on Thursday.

CNN reported, however, that another aide to Mr. Rouhani had told Ms. Amanpour “that while the president does not tweet from his account, people in his office do, so it is semi-official.”

Earlier in the week, Iranian officials claimed that another former president, Ali Akbar Hashemi Rafsanjani, had been misquoted by a local news agency which reported that he said the people of Syria “have been the target of chemical attacks by their own government and now they must also wait for an attack by foreigners.” As Monavar Khalaj explained in The Financial Times, however, those denials seemed to be undercut by an audio recording of what sounded very like Mr. Rafsanjani making just those remarks which appeared online Tuesday.

Dan Bilefsky contributed reporting.