More governments aim to censor the internet, according to the US State Department's annual report on human rights.
US secretary of state Hillary Clinton said more governments were imposing "new and crippling restrictions" on non-government organisations that try to protect rights and enhance accountability.
"New technologies have proven useful both to oppressors and to those who struggle to expose the failures and the cowardice of the oppressors," she said.
The report said more people gained greater access than ever in 2009 to more information about human rights through the internet, cell phones, and other forms of connective technologies.
"Yet it was a year in which governments spent more time, money, and attention finding regulatory and technical means to curtail freedom of expression on the internet and the flow of critical information and to infringe on the personal privacy rights of those who used these rapidly evolving technologies," it said.
These comments came as Google launched a day of protest against online censorship on YouTube, its free-to-view video website. The move comes less than a week after Google UK's CEO warned that changes to the UK's Digital Economy Bill could stop online free speech.
Google director of public policy Robert Boorstin said in an official Google blog post that 40 countries had censored online free speech, adding that 25 had blocked Google and YouTube.
"More than ever, governments around the world are threatening online free expression," he said.
This week Google UK managing director Matt Brittin was one of 16 signatories to a letter that warned that Amendment 120a to the Digital Economy Bill could stifle online free speech while doing nothing to stop illegal file-sharing.
Amendment 120a would go far to give effect to proposals in the international anti-counterfeiting trade agreement (Acta) being negotiated in secret to stop international trade in counterfeit and pirated goods.
The European Parliament voted this week by more than 660 to 13 against the Acta provisions to allow a "three strikes" clause to disconnect alleged illegal file-sharers and the search and seizure of personal goods at borders.
Google last night sponsored the first Netizen Prize (or "Le Prix de Net Citoyen") awarded by the Paris-based advocacy group Reporters Without Borders.
The award was won by the Iranian creators of the website Change for Equality. The site was set up in 2006 to fight for changes in Iranian laws that discriminate against women. The site has become a source of information on women's rights in Iran, documenting arrests of women activists and becoming a rallying point for opponents of the government.