A Vietnamese journalist who exposed police corruption has gone on trial for offering a bribe that he says was part of his investigation.

The state-run Tuoi Tre newspaper says its reporter Hoang Khuong is accused of offering a police officer a bribe of $710.

Khuong's undercover investigation series last year triggered public anger about police corruption and led to the arrest of the officer who allegedly accepted the bribe.

Thursday's Tuoi Tre newspaper quotes Khuong as telling police he was doing his job as a journalist and had no personal gain as a result of bribing the officer, who is standing trial alongside Khuong and three other people. Khuong's arrest in January was condemned by the international journalist watchdog Reporters Without Borders.

Khuong faces 13 years in jail if convicted.