SAN FRANCISCO/WASHINGTON - Islamic State's Twitter users, which have trumpeted the group's violent acts and worldview on the social media service, have gone abruptly quiet in past days.
Several accounts affiliated with the militant group appear to have gone dormant, according to US government sources, raising questions about whether the government has pressured Twitter to clamp down more aggressively or whether the group has moved to other social media channels.
When contacted, several US officials said on condition of anonymity they were unaware of attempts to quash those Twitter accounts. The sudden silence also came days after reports about Islamic State-linked accounts threatening action against Twitter employees, though there was no evidence to link the two episodes.
Twitter Inc declined to comment on actions the company has taken related to accounts affiliated with the group, which is also known as the Islamic State in Iraq and Syria and as the Islamic State of Iraq and the Levant.
But it has suspended several accounts affiliated with the group in recent months, including one user who threatened retaliation against Twitter's employees.
A US official who spoke on condition of anonymity said that as government officials identify people on social media whom they believe to be "terrorists" or "extremists," they draw them to the attention of companies such as Twitter and Facebook Inc, which act at their own discretion.
"People (in government), but also people outside, are constantly referring these companies to identified terrorists," the official said. "I wouldn't say there is a systematic policy that the US government is going around asking (companies like) Twitter to shut these people down. They sprout very fast. They change their handles."
A second government source familiar with the situation said there was a clear change of social media tactics by Islamic State in the days leading up to President Barack Obama's Wednesday speech. Obama said then that he had authorised air strikes in Syria and Iraq, in a broad escalation of a campaign against the organisation.
Some experts say the militants may have increasingly taken to other online services such as Russia's VKontakte and Diaspora, a four-year-old social network that relies on a decentralized network of independent computer servers.
Such a tactic is sometimes employed when militants want to evade tracking, the source added.