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

Both Iran's new president, Hasan Rouhani, and 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.

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