Hassan Rouhani, Iran’s president, gestures to the media during a news conference in Tehran in this June 2013 photo. (Fars News/Reuters)

A series of tweets by Iranian leaders over the past couple of days has students of diplomatic semantics — a sometimes exact science — wondering whether a mere greeting is an opening to the country’s adversaries.

Both Iran’s new president, Hassan Rouhani, and the new foreign minister, Mohammad Javad Zarif, sent Rosh Hashanah greetings via Twitter to Jews celebrating the new year.

Rouhani also announced Thursday that nuclear negotiations will be run by the Foreign Ministry, headed by Zarif, a U.S.-educated diplomat and former long-serving Iranian ambassador to the United Nations who is familiar to many U.S. officials.

Both the tweets and Zarif’s portfolio represent an intriguing break with the tone and approach of former Iranian leader Mahmoud Ahmadinejad and come ahead of Rouhani’s international debut at the United Nations this month.

State Department spokeswoman Jennifer Psaki said the United States hopes the move signals a willingness to “engage substantively,” and if so, she said, Iran “will find a willing partner in the United States.”

“The inauguration of President Rouhani presents an opportunity for Iran to act quickly to resolve the international community’s deep concerns over Iran’s nuclear program,” Psaki said.

Javier Solana, who led negotiations with Iran as the top European Union diplomat, took to Twitter on Thursday to praise Rouhani and Zarif for their messages: “Iran’s new pres & FM new to Twitter: Let’s hope they bring new policies, boosting chance of peace.”

Haleh Esfandiari, an Iranian-born scholar at the Wilson Center, called the Iranian leaders’ engagement on Twitter “a breath of fresh air after eight years of Ahmadinejad.”

Rouhani finds Twitter to be a helpful tool to get a message outside Iran and uses it expressly for that purpose, Esfandiari said. It works, she said. “I’m waiting to see when the commanders of the Revolutionary Guard will start tweeting in English too.”

Some analysts were more skeptical, noting that control of nuclear policy ultimately rests with Iran’s supreme leader, Ayatollah Ali Khamenei. While other nations involved in long-running, and largely fruitless, negotiations over Iran’s disputed nuclear program run the talks out of their foreign ministries, Ahmadinejad had dispatched a separate national security council group to speak for him.

“The one advantage of the Supreme National Security Council conducting negotiations is that it represented all institutions of the government,” including the supreme leader, said Ray Takeyh, an Iran scholar at the Council on Foreign Relations.

On Wednesday evening, Rouhani — or whoever handles his English-language Twitter account — wished all Jews a happy Jewish New year. He took special note of Iran’s anciently rooted Jewish community.

“As the sun is about to set here in Tehran I wish all Jews, especially Iranian Jews, a blessed Rosh Hashanah.”

A day later, as the message was analyzed abroad and in Iran, the semi­official Fars news agency quoted a Rouhani aide as saying that the account was no longer active. That appeared to be a dodge, especially since the same account was also used Thursday to announce the change in Iran’s nuclear negotiating team.

The posting Thursday linked to the announcement on Rouhani’s Web site that the Foreign Ministry will conduct future talks over Iran’s nuclear program.

“Only way to interact w/ Iran is dialogue on equal footing, ­confidence-building & mutual respect as well as reducing antagonism & aggression,” the @HassanRouhani account added a little later, repeating a common Iranian negotiating stance.

Zarif’s new year’s greeting followed shortly after Rouhani’s and led to a polite and spirited back and forth with Christine Pelosi, a California author, political activist and daughter of House Democratic leader Nancy Pelosi.

“Thanks. The New Year would be even sweeter if you would end Iran’s Holocaust denial, sir,” Pelosi wrote.

“Iran never denied it,” Zarif replied Thursday. “The man who was perceived to be denying it is now gone. Happy New Year.”

That was a reference to Ahmadinejad. Considered a moderate with close ties to members of Iran’s reform movement, Zarif is known to have a dry sense of humor. His Twitter account, which is linked to Rouhani’s, notes that he holds a degree from the University of Denver.

“Zarif is probably the most sophisticated and effective diplomat Iran has had since the 1979 revolution,” said Karim Sadjadpour, an Iran scholar at the Carnegie Endowment for International Peace. “He presents a double-edged sword to the West and Israel: Iran is easier to engage but more difficult to isolate with Zarif as foreign minister.”

While Twitter and other social-networking sites are blocked in Iran, Rouhani has used the popular microblogging site, and the same account, since early in his presidential campaign to share campaign platforms and publicize important policy decisions.

The tweet Wednesday directed at Jews was a major public departure for Iran’s leadership. Although the Islamic republic has long opposed the state of Israel, or the “Zionist regime” as it is known here, Iran is home to the largest community of Jews in the Middle East outside Israel and provides a seat in the country’s parliament for a Jewish lawmaker.

Neither message by the Iranian officials mentioned Israel or Iran’s long enmity with the Jewish state, but coming weeks before Rouhani will speak at the U.N. General Assembly, the good wishes were striking. Ahmadinejad regularly used his annual U.N. appearance as a platform to question Israel’s legitimacy.

Rouhani and President Obama are scheduled to address the United Nations on Sept. 24, as the United States and other world powers consider a new round of talks with Iran aimed at averting what the West claims is a drive for a nuclear bomb. Iran denies that it has such a goal.

Previously, Iran’s Supreme National Security Council handled the country’s nuclear negotiations. Iran’s negotiating team was led since 2007 by Saeed Jalili, an ultraconservative who was considered an early front-runner in Iran’s June presidential election.

Jalili, in particular, is associated with a policy that Iranian leaders should continue to adhere to the ideological tenets of Ayatollah Khomeini, who founded the Islamic republic in 1979.

One of these guiding principles is Iran’s strong anti-U.S. policy, which has been a major barrier to attempts to find a diplomatic solution to the country’s contested nuclear ambitions.

Moving the nuclear file to the Foreign Ministry is a sign that Rouhani intends to make good on his campaign promise of mending Iran’s relations with other countries and enhancing its image abroad.

Nuclear negotiations have made little progress in recent years, while Iran has pressed ahead with uranium enrichment that Israel claims is edging close to a level sufficient to build weapons.

Gearan reported from Washington.