An Internet watchdog has accused Ethiopia of blocking scores of anti-government websites and millions of blogs.
The OpenNet Initiative said the country was stopping citizens from viewing opposition-linked sites and blogs hosted by Blogger, an online journal community owned by Google.
Ethiopia dismissed the report as "a baseless allegation".
"We may have technical problems from time to time," an information ministry spokesman said. "But we have not done anything like that, and we have no intention of doing anything like that."
The OpenNet Initiative - a partnership between Harvard Law School, and universities of Toronto and Cambridge and Oxford - said it had gathered proof of interference.
"We have run diagnostic tests using volunteers in Ethiopia which indicate that they are blocking IP addresses," OpenNet research director Robert Faris said, referring to the unique numeric addresses of Web sites.
"The evidence is overwhelming that that is what they are doing. Most of the sites that we found blocked were related to freedom of expression, human rights and political opposition," he said.
The allegations could be embarrassing for the Ethiopian government, which is a major ally of the United States in Africa and has been criticised for a post-election crackdown on opposition that killed nearly 200 people in 2005.