HANOI (AFP) — Observers from a global association of lawyers were barred last week from a controversial Vietnamese trial at which four dissidents were jailed, the group said Saturday.

The International Bar Association's (IBA's) Human Rights Institute said two observers it sent to monitor the trial Wednesday in Ho Chi Minh City were not allowed into the court, despite diplomatic intervention.

"The observers were then subsequently interrogated by immigration authorities," the group said in a statement.

It said that international conventions to which Vietnam is a party provide for the right to a fair and public trial, and expressed grave concerns at the observers' exclusion.

"The practice of sending trial observers is well established and accepted in the international community. The presence of impartial and independent observers helps facilitate the proper functioning of the court process and helps guarantee the right to a fair trial," said Martin Solc, co-chairman of the rights institute, a division of the London-based IBA which represents 30,000 lawyers around the world.

Some diplomats and foreign journalists were permitted to monitor the one-day trial from a separate room via closed-circuit television whose sound was sometimes difficult to understand.

Internet entrepreneur Tran Huynh Duy Thuc, 43, was sentenced to 16 years in prison while blogger Nguyen Tien Trung, 26, received seven years. Human rights lawyer Le Cong Dinh, 41, and Le Thang Long, 42, were each given five years.

Their convictions, for trying to overthrow the communist state, prompted criticism from the European Union, the US ambassador, and a British minister.

Vietnam's foreign ministry responded late Friday that the case was handled in accordance with Vietnamese and international law. It accused foreigners of intervening in the country's affairs.

A commentary about the case Saturday in the Quan Doi Nhan Dan (People's Army) daily said foreign newspapers had published articles which showed "a biased attitude towards the Vietnamese state and also an over-intervention into the internal affairs of an independent country."