Hours before US Secretary of State Antony Blinken’s visit to Hanoi, the US criticised Vietnam’s imprisonment of a major political activist, saying relations could only be fully realized if the country addressed its human rights record.

A Hanoi court sentenced Nguyen Lan Thang to six years in prison on Wednesday for anti-state actions, according to his lawyer, in a case that has sparked international concern over communist-ruled Vietnam’s treatment of dissidents.

Thang participated in environmental and anti-China protests, voiced support for jailed activists, and blogged about socio-political issues, according to his social media accounts.

“We urge the Vietnamese government to immediately release and drop all charges against Nguyen Lan Thang and other individuals who remain in detention for peacefully exercising and promoting human rights,” a State Department spokesperson said.

“Ahead of the secretary’s visit to Hanoi, our message is clear – Vietnam is an important partner in the Indo-Pacific, and that partnership can only reach its full potential if the government of Vietnam takes concerted steps to meet its obligations and commitments under international law and improve its human rights record,” the spokesperson added.

Vietnamese authorities have convicted at least 163 people since 2018 for exercising their rights to freedom of expression or association under “vague or over-broad laws that criminalize protesting or criticizing the government”, according to Human Rights Watch.

In a statement on Thursday, Human Rights Watch called on Blinken, who is due in Hanoi on Friday, to “publicly and privately urge Vietnam’s leadership to end its systemic abuse of freedom of expression, association, and peaceful assembly.”

Blinken is making his first trip to Vietnam as secretary of state, hoping for progress towards upgrading relations with a key trade partner that shares U.S. worries about China’s growing might.