A well-known Vietnamese political blogger has had his website hacked in what a Western diplomat described as a more aggressive approach by authorities to online critics.
"My personal blog has been attacked for several days by hackers and is no longer accessible," said Huy Duc, whose blog, "Osin", could not be opened.
Duc said he did not know what the problem was but a Western diplomat said the authorities appeared to be behind recent problems at a number of politically-oriented and critical websites.
Analysts, rights groups and diplomats say the human rights situation in Vietnam has been worsening.
"In the past month or two there have been at least 10 websites that have been hacked or taken down," said the diplomat, asking not to be named.
While some have been able to get back online, the authorities are "trying to be more aggressive," the diplomat said.
The Vietnamese government would not immediately respond to a request for comment.
Western donors took Vietnam to task in December, saying its restrictions on news media and internet sites such as Facebook threatened its rapid economic progress.
Duc was fired last August from his job as a reporter for the newspaper Sai Gon Tiep Thi (Saigon Marketing) after comments in his blog that highlighted human rights abuses by the communist Soviet Union.
Other posts by Duc, a veteran journalist and former soldier, criticised government responses to major issues including corruption, relations with China, and treatment of the media.