By MARK LANDLER
Mr. Kerry wasted no time putting his handle to work, posting a blunt 106-character message that condemned the Syrian government for using barrel bombs on apartment houses and a mosque in Aleppo. Hours earlier, Mr. Kerry had issued a statement that did the same thing, but ran on for three paragraphs and used the word “communiqué.”
The next iteration of Twitter diplomacy has arrived — one that involves augmenting, sometimes even replacing, the carefully scripted and vetted language of official State Department and White House statements with the choppy patois of Twitter.
The national security adviser, Susan E. Rice, and the American ambassador to the United Nations, Samantha Power, both regularly write posts responding to grave issues, from the imprisonment of a Chinese legal scholar to atrocities in the Central African Republic.
Then there is Michael A. McFaul, a former White House aide who pioneered the use of Twitter as a diplomatic tool when he became ambassador to Russia in 2011. Mr. McFaul announced his departure on Tuesday — in a blog post — and then spent the rest of the day accepting good wishes on Twitter.
“Don’t think going back to Cali means I won’t call for advice,” Mr. Kerry wrote on Twitter to Mr. McFaul, who has been a professor at Stanford and is reuniting with his family in California.
Mr. McFaul’s posts landed him in hot water with the Russian government early in his tenure, when he defended protesters and expressed suspicion that he was under surveillance by the local authorities. But he kept at it, posting in both English and Russian. Twitter, he said Tuesday, allowed him to “interact with a high school student in Vladivostok or a minister in the Russian government almost instantaneously,” without having to go through the Russian news media.
Other ambassadors followed his example, notably Caroline Kennedy, who raised hackles in Japan by writing critically about the bloody but traditional practice of dolphin hunting there.
While tweeting ambassadors are no longer novel — the State Department now expects envoys to have a visible web presence — the phenomenon of top officials posting about American policy on delicate issues takes digital diplomacy to a new level. It also raises new risks, since an ill-considered post by Mr. Kerry about the Middle East is potentially a bigger headache than Ms. Kennedy’s views on dolphins.
“It won’t be a substitute for a meeting or a substitute for a phone call,” said Douglas Frantz, the assistant secretary of state for public affairs. “American foreign policy is probably too nuanced to explain in 140 characters. It will be used to deliver quick messages and amplify existing messages.”
The status of these messengers is not lost on foreign audiences, said P. J. Crowley, one of Mr. Frantz’s predecessors at the State Department. “There is potential value in John Kerry and Susan Rice tweeting in their own names,” he said. “Perhaps their words aren’t so important as the fact that they are personally involved.”
The challenge, Mr. Crowley said, will be to figure out a strategic purpose for their tweeting. “It will be interesting to see what lessons Caroline Kennedy draws from her tweets about the dolphin hunt, which accurately reflected American policy, certainly began an earnest two-way conversation about these issues and opened a hornet’s nest,” he said.
Ms. Rice, who began posting as ambassador to the United Nations, has said that she initially worried about practicing foreign policy by haiku. But she discovered that the brevity of Twitter forced her to distill the government’s message to its essence. It has also served as a diplomat’s equivalent of rapid response.
“When you have an emerging issue or narrative out there, sometimes the best way to push against it is to get out there,” said Patrick Ventrell, a spokesman for the National Security Council. “These are not just missives fired off in the heat of the moment.”
A case in point came Monday night, when Ms. Rice fired off a series of indignant posts in defense of Mr. Kerry, who had come under fire from Israeli officials for suggesting that a failure in the Israeli-Palestinian peace negotiations could stoke a movement to boycott Israeli products and deny legitimacy to Israel.
“Personal attacks in Israel directed at Sec Kerry totally unfounded and unacceptable,” Ms. Rice wrote.
“John Kerry’s record of support for Israel’s security and prosperity rock solid,” she also posted.
Alec J. Ross, who helped devise digital diplomacy initiatives for Mr. Kerry’s predecessor, Hillary Rodham Clinton, said the greatest value of Twitter for senior officials was in gathering intelligence, not sending messages.
Whatever the risks, American officials may feel they have no choice but to tweet, since so many of their foreign counterparts are doing it. President Hassan Rouhani of Iran scooped the White House by posting about his historic phone call with President Obama last fall.
Mr. Kerry, who maintained a chatty Twitter account as a senator, would have liked just to keep using it. But his aides persuaded him to use the more formal State Department account for the first year, signing his posts with initials, Mr. Frantz said.
What is the most immediate risk from an unleashed Mr. Kerry? “A lot of foreign ministers are going to learn more about the Boston Bruins than they ever imagined,” Mr. Frantz said.
