US Secretary of State Hillary Clinton has warned repressive governments not to restrict internet freedom, saying such efforts will ultimately fail.
She said the US was committed to global internet freedom, in her first major address since the Egyptian uprising.
The speech comes as online activists organise anti-government protests in several Middle Eastern countries.
"This is a foreign policy priority, one that will only increase in importance in the coming years," Mrs Clinton said.
In what is being hailed as a major policy speech, Mrs Clinton announced that the US government would invest an additional $25m (£15m) to help online dissidents and digital activists fight state repression.
She named China, Syria, Cuba, Vietnam and Burma as countries restricting online speech, and noted that Egypt's attempt to stifle protesters by switching off the internet was unsuccessful.
Social networking sites like Twitter and Facebook were important tools that gave voice to people's aspirations, Mrs Clinton said.
She said the US state department would start Twitter accounts in Chinese, Russian and Hindi, adding to a suite of feeds that already includes French, Spanish, Arabic and Farsi.
She acknowledged that the internet has a problem with hateful speech which can inflame hostilities, but said that efforts to curb such content often become an excuse to violate rights to free speech.
"The best answer to offensive speech is more speech. People can and should speak out against intolerance and hatred," she said.
Mrs Clinton also linked internet freedom with economic prosperity.
Mrs Clinton's speech comes amid a divisive debate in the US over the leaking of thousands of classified government documents to Wikileaks.
She drew a sharp distinction between Wikileaks' possession of secret government correspondence and internet freedom.
"Fundamentally, the Wikileaks incident began with an act of theft," Mrs Clinton said. "Government documents were stolen, just the same as if they had been smuggled out in a briefcase."
She pushed back against critics who argue that government should conduct all its work openly and transparently.
"The United States could neither provide for our citizens' security nor promote the cause of human rights and democracy around the world if we had to make public every step of our most sensitive operations," she said.