The United Nations rights agency on Friday expressed deep concern over the jailing of four rights and land activists in Vietnam and demanded their immediate release.

The communist regime often moves swiftly to stifle dissent, jailing activists, journalists and any critic with large audiences on Facebook.

"We are deeply troubled by the harsh sentencing of human rights and land rights defenders convicted of spreading anti-state propaganda in Vietnam," Ravina Shamdasani, a spokeswoman for the UN High Commissioner for Human Rights, said.

"In the span of three days this week, four prominent human rights defenders... were sentenced to up to 10 years in jail and five years on probation," she said.

"All the cases follow similar worrying patterns that raise serious issues concerning the presumption of innocence, the legality of their detention, and the fairness of their trial," she said.

"We urge the authorities in Vietnam to immediately release all these individuals as well as the many others arbitrarily detained".

Do Nam Trung, well known for taking part in environmental and anti-China protests and opposing government corruption, was sentenced on Thursday to 10 years in jail. 

Activists Trinh Ba Phuong and Nguyen Thi Tam were sentenced a day earlier to 10 years and six years in jail respectively on the same charge.

On Tuesday, one of Vietnam's most prominent dissident journalists Pham Doan Trang was sentenced to nine years behind bars on anti-state charges.

The UNHCR spokeswoman called on Vietnam "to repeal all legal provisions that violate fundamental freedoms", saying the charges brought against the four were "vague and overly broad and thereby inconsistent with international human rights norms".