Freedom House, which examined web freedom issues in 15 countries, listed Cuba, Iran and Tunisia as three other nations it considered "not free" due to government control of online activity.
Seven countries studied — Egypt, India, Georgia, Kenya, Malaysia, Russia and Turkey — were considered "partly free" while four others — Brazil, Britain, Estonia and South Africa — were labeled "free."
Freedom House, which monitors political rights and civil liberties around the globe, said the rights of Internet users were increasingly at risk as governments expanded their ability to control online activity.
"More than a billion people look to the Internet and mobile phones to provide a new freedom frontier, where they can exercise their right to freedom of expression without repercussion," Freedom House executive director Jennifer Windsor said in a statement.
"But as access grows, more governments are employing diverse and sophisticated methods to monitor, censor and punish Internet users."
In its report, "Freedom on the Net," to be formally released later Wednesday at a conference of bloggers in Berlin, Freedom House evaluated the 15 countries based on barriers to Internet access, limitations on content and violations of users' rights.
The Washington-based group said Cuba received the lowest score in the study.
"Cuba is one of the world's most repressive environments for Internet freedom, despite a slight relaxation of restrictions on computer and mobile phone sales in 2008," it said.
"There is almost no access to Internet applications other than e-mail and surveillance is extensive. Cuba is one of the few countries with laws and regulations explicitly restricting and outlawing certain online activities."
Freedom House also said that China and Cuba were tied for curbing the most users' rights.
China has the world's most Internet users, an estimated 300 million, but "also has the world's most highly-developed censorship apparatus," it said.
The report cited "sophisticated and multilayered system" used by Chinese authorities to censor, monitor and control Internet and mobile telephone activities.
It also mentioned the "hundreds of thousands" of people authorities and private providers employ to "monitor, censor and manipulate online content."
But "due to the egalitarian nature and technical flexibility of the Internet, the online environment remains more free than traditional media," Freedom House said.
Iran, the report said, "uses a complex system of nationwide content filtering, intimidation, detention and torture of bloggers, and restriction of broadband access to subvert freedom of expression online."
Freedom House was created in 1941 by Eleanor Roosevelt, wife of then US president Franklin Roosevelt, among others. It receives funding from the US government and private organizations.
