The surprise first phone contact Friday between presidents Barack Obama and Hassan Rouhani was not only a dramatic moment in US-Iranian ties, but also in the field of digital diplomacy.
US President Barack Obama speaks to members of the press in the briefing room of the White House September 27, 2013 in Washington, DC about a phone conversation he had with Iranian President Hassan Rouhani
Moments before the US leader announced from the White House podium that he had had a chat with his opposite number, the Iranian president had sent a tweet that may well live on in history.
"In a phone conversation b/w #Iranian & #US Presidents just now: @HassanRouhani: 'Have a Nice Day!' @BarackObama: 'Thank you. Khodahafez,'" it read.
Khodahafez is a Farsi phrase used on parting, like "farewell" or "goodbye," but literally translated as "God be your protector."
Rouhani's account appeared on Twitter after his election this year and his English-language messages have become a symbol of Tehran's diplomatic outreach.
There has been some controversy about the account in Iran. It has not been officially confirmed as his and social networking sites are banned to ordinary citizens.
But throughout his visit this week to the UN General Assembly in New York, Rouhani's office has used the stream to keep followers up to date with his speeches and media appearances.
Any lingering doubts that the account is indeed run by his office evaporated when it confirmed the phone call before the White House did.
And on Friday, even as Obama spoke in the more traditional venue of the White House briefing room, Rouhani outlined his side of the exchange online.
"President #Rouhani and President @BarackObama expressed their mutual political #will to rapidly solve the #nuclear issue," he said, in a stream of messages sent as his car headed to the airport to leave the US.
"Obama, @HassanRouhani appoint Foreign Ministers to follow up cooperation ASAP.
"@BarackObama to @HassanRouhani: I express my respect for you and ppl of #Iran. I'm convinced that relations between Iran and US..1/3
"@HassanRouhani to @BarackObama: We're hopeful about what we will see from P5+1 and your govt in particular in coming weeks and months..2/3
"@HassanRouhani to @BarackObama: I express my gratitude for your #hospitality and your phone call. Have a good day Mr President. 3/3
"@BarackObama to @HassanRouhani: Thank you, Khodahafez."
Later, for reasons that were not immediately clear, many of the tweets were deleted -- although not before they had been recorded as screenshots or retweeted by thousands of Web users.
The messages that remained, which White House officials confirmed appeared to be both genuine and to reflect a shared understanding of the tone of the call, recounted a cordial exchange.
And the Iranian presidency, in what was certainly an unprecedented gesture, even retweeted on their own account a message from US Secretary of State John Kerry.
"Good first steps w/ #Iran this wk. Positive meeting w/ @JZarif last night. Historic POTUS and @HassanRouhani call today. #Progress -JK," said the State Department account.
Regular Twitter users know that a retweet is not necessarily an endorsement, but the fact that Kerry's message survived the later purge suggests that Rouhani shared his positive take.
The tweets raced around the world and stunned many observers -- not all of them disinterested figures -- who sensed that history was being made.
"I feel like I'm witnessing a tectonic shift in the geo-political landscape reading @HassanRouhani tweets. Fascinating," tweeted Twitter chief executive Dick Costolo.
Costolo doubtless had his reasons to celebrate his own platform's role in the incident -- but there was a sign that he might have a point: Rouhani retweeted him.