Pham Doan Trang was arrested on Friday evening, Nguyen Anh Tuan, editor in chief of VietnamNet, told AFP.

He said officers of the national security department told him that "she violated national security" for activities unrelated to her work.

"Don't link it to her articles and her work on VietnamNet," said Tuan, whose website publishes in Vietnamese and English.

Tuan said he did not know where the arrest occurred or where Trang, aged about 31, was now. He said he had not been able to contact her.

Trang had written a "little bit" about maritime sovereignty issues in the South China Sea, where Vietnam and China are engaged in a boundary dispute.

Other writing had discussed the 1954 Geneva Conference, which led to Vietnam's division, but Tuan said: "Any article she wrote on VietnamNet I think is no problem."

She was arrested a day after Bui Thanh Hieu, who blogs under the name Nguoi Buon Gio, was arrested over issues of "national security", a member of his family said.

Recent posts on his blog commented on the Vietnam-China maritime sovereignty dispute, on a controversial bauxite mining project in the Central Highlands, and criticised the recent arrests of human rights lawyer Le Cong Dinh and others.

US ambassador Michael Michalak last week expressed concern over those arrests as well as communist Vietnam's efforts to crack down on the media and to "criminalise free speech".

Analysts saw Dinh's arrest in May as part of a long-running crackdown. Some critics and observers said the arrest of him and the others was partly a message to those who see the government as too accommodating towards China on border disputes and mining.

In May Trang wrote on VietnamNet that China "possesses the conditions to become a regional hegemonist."

Last week, Vietnamese newspaper reporter Huy Duc was fired after writing comments in a personal blog highlighting human rights abuses committed by Vietnam's former communist ally the Soviet Union.

Agence France Presse - September 1st, 2009