A popular pro-Tamil Tiger website says it has been blocked in Sri Lanka.
The Tigers are fighting for an independent Tamil homeland
Reports from Colombo say the TamilNet website, which is regularly checked by diplomats and journalists, can no longer be accessed.
It is not clear who has blocked it or why, but the website, and independent media campaigners, said the government was to blame.
Government Information Director Anusha Pelpita denied any knowledge of the site having been blocked.
TamilNet is a popular source of information for the substantial Tamil diaspora thousands of miles away in Europe and North America.
Attempts to access the site in Sri Lanka have mostly thrown up error reports.
The media rights group Free Media Movement said all major internet service providers had blocked the site on government orders, the Associated Press reported.
"This is a significant turn in the erosion of media freedom in Sri Lanka and clearly demonstrates the extent to which media is censored and the free flow of information curtailed, without any accountability, transparency or judicial oversight," the group said in a statement.
"The ban on TamilNet is the first instance of what the Free Media Movement believes may soon be a slippery slope of web and internet censorship in Sri Lanka," it said.
Tamil Tiger rebels have been fighting for independence from Sri Lanka since 1972.
Around 60,000 people are reported to have been killed in the conflict.