Vietnam sentenced a music teacher to 11 years in prison on Friday for Facebook posts that allegedly undermined the one-party state, which has been accused of tightening the noose on online dissent. Communist Vietnam has long jailed its critics but has come under fire recently for targeting users on Facebook, a popular forum for activists in the country where all independent media is banned. Nguyen Nang Tinh is the latest activist jailed for his Facebook comments, including posts about police brutality, land rights, and a Taiwanese steel firm that dumped toxic sludge into the ocean, killing masses of fish off the coast of Vietnam. Authorities accused the college music teacher of posting "hostile thoughts" and "profound anti-government material" on social media. The 42-year-old was sentenced to 11 years for "producing, disseminating or spreading information and documents aimed at undermining" Vietnam, his lawyer Nguyen Van Mieng told AFP from central Nghe An province. He got another five years probation. The jail term was "too harsh", Mieng told AFP, arguing that prosecutors did not have sufficient evidence. Tinh's father Nguyen Ngoc Dinh insisted his son was innocent, saying he "only raised his voice against injustice in society". - Missing activist - Tinh's conviction Friday came as another activist was held for eight hours at Hanoi's airport as she arrived from Thailand. Dinh Thao is a pro-democracy campaigner and vocal critic of Vietnam's communist regime who lived abroad and worked for a Vietnamese civil society organisation. Her husband Phillip said she came back to help fellow activists in the country, but he lost touch soon after her arrival on Friday. Security officials asked Thao about her work and confiscated her passport before releasing her in Vietnam, he told AFP, providing his name only as Phillip. Human Rights Watch and Amnesty International earlier decried her detention, while immigration police refused to comment to AFP. The news came just days after a dissident with Australian citizenship was jailed for 12 years in Vietnam on terrorism charges, along with two other Vietnamese nationals who got 10 and 11 years. Vietnam is accused of cracking down on activists since a conservative leadership came to power in 2016. A cybersecurity bill passed last year -- and not yet implemented -- requires sites like Facebook and YouTube to remove content if asked by the government to do so. The controversial law would also require companies to hand over user data and host servers in the country. Amnesty International says there are at least 128 political prisoners behind bars in Vietnam, 10 percent it estimates were jailed for Facebook posts. Other rights groups put the number of jailed dissidents as far higher, but no official data is available.