HANOI (AFP) -- Vietnam on Friday jailed a blogger who posted critical material on Facebook for five years, his second sentence in less than a month as a hardline administration tightens its grip on dissent.

More than 50 activists, rights campaigners and bloggers have been put behind bars in 2018, in one of the harshest crackdowns in years.

Observers say a conservative administration in charge since 2016 is behind the sweeping campaign, which shows few signs of easing.

Citizen journalist Do Cong Duong used Facebook to voice his opinions on a number of hot-button issues and was jailed in connection with posts that included criticism of corruption and land disputes.

He was sentenced to five years in prison for “abusing democratic freedoms”, his lawyer Ha Huy Son told AFP.

“Duong admitted to fighting against corruption and injustice, asking that the rights of people be respected. But he said he did nothing against the party (or) the state,” Son said after the half-day trial in northern Bac Ninh province.

“They... put him in jail as a warning message,” added Son.

Land is a sensitive topic in Vietnam, where rapid urbanisation and breakneck development have squeezed poor families especially in rural areas. 

Duong was jailed last month for four years for disturbing public order for filming forced evictions, and will now serve a total of nine years.

Like many activists in the one-party state where all independent media is banned, Facebook was Duong‘s primary outlet.

The communist regime allows but closely monitors social media platforms.

But a new cybersecurity law set to come into effect in January threatens to police anti-government content on the site and muzzle critics.

The law requires internet providers like Facebook and Google to remove content and hand over user data if requested by the government to do so.

Facebook and Google have not said whether they will comply with the law.

At least 55 dissidents have been jailed in Vietnam this year according to an AFP tally, a spike from 29 arrested last year as reported by Amnesty International.

Rights groups fear the harsh clampdown could accelerate with ultraconservative Communist Party Chief Nguyen Phu Trong slated to become president in coming weeks.

In his dual role as head of party and head of state, Trong will be the most powerful person in the country and analysts say he will face little opposition implementing his agenda, which also includes an unprecedented anti-corruption drive.

“Hanoi seems determined to put every dissident it can behind bars so the international community needs to get off the sidelines and stand up now against this wave of repression,” said Phil Robertson, deputy Asia director at Human Rights Watch.