"The United States believes passionately and strongly in the basic principle of free expression," Clinton told reporters when asked about the State Department's request to the social networking firm Twitter.
"We promote the right of free expression," the chief US diplomat added.
"And it is the case that one of the means of expression, the use of Twitter is a very important one, not only to the Iranian people but now increasingly to people around the world, and most particularly to young people," she said.
"I wouldn't know a twitter from a tweeter, but apparently it is very important," she said, sparking laughter.
"And I think keeping that line of communications open and enabling people to share information, particularly at a time when there was not many other sources of information, is an important expression of the right to speak out and to be able to organize," she said.
The US government took the unusual step of asking Twitter to delay a planned maintenance outage because of its use as a communications tool by Iranians following their disputed election, a senior official said Tuesday.
The request highlighted the Obama administration's Web-savvy and the power of social networks such as Twitter and Facebook in organizing protests over the election results in the face of a ban by Iranian authorities on other media.
But it also seemed to run counter to President Barack Obama's public efforts not to appear to be meddling in Iran's internal affairs.
Twitter delayed Monday's scheduled tune up, which would have taken place during daylight hours in Iran, and rescheduled it for Tuesday but said the decision was made with its network provider, not the State Department.