HANOI (AFP) - A Vietnamese court has jailed nine people for "attempting to overthrow the state", official media reported on Friday (Dec 29), the latest heavy sentence doled out in a harsh crackdown this year against activists in the one-party state.

Communist Vietnam routinely jails its critics, but 2017 has been particularly grim for dissidents, with at least 15 arrested and several others sentenced to lengthy prison terms.

Nine people were convicted on Thursday for attempting to overthrow the government and for anti-state propaganda - a charge rights groups have slammed for being vaguely worded and used to crush dissent - in central Binh Dinh province.

They were accused of distributing leaflets "defaming leaders and calling for the government to be overthrown", according to an online report on Friday from ANTV, the official police television channel, citing the indictment.

Ta Tan Loc, 42, was sentenced to 14 years in prison, while his eight accomplices got between three and 13 years, ANTV reported.

The court accused the group of having links to an overseas "reactionary" group, the channel added, without providing details.

Vietnam's government is accused of scaling up arrests and convictions of critics since a new conservative leadership took control last year.

Some observers have said the US withdrawal earlier this year from the Trans-Pacific Partnership - a sprawling multinational trade agreement - also removed incentives for the Vietnamese government to ease up on dissidents.

Amnesty International reports that at least 15 people have arrested this year, though several other activists have been convicted and jailed, joining scores of activists already in prison.

All independent media is banned in Vietnam, and the government has called for increased internet control as critics have moved onto social media to voice discontent.

A top general said this week that 10,000 cyber-warriors have been deployed to fight "wrongful views" and anti-state propaganda online, a move decried by rights groups.