The Committee to Protect Journalists has joined 52 other civil society groups in calling on United Nations High Commissioner for Human Rights Volker Türk to address systemic abuses occurring in Hong Kong’s prisons.

The joint letter highlights serious violations documented in a recent report, including the use of solitary confinement lasting far beyond international limits, and chronic medical neglect that has led to severe health problems and preventable deaths.

Seven journalists are among more than 700 political prisoners languishing in Hong Kong’s prisons. The most prominent of which is 77-year-old media publisher Jimmy Lai, who has been jailed for nearly five years, mostly in solitary confinement, and is awaiting a verdict on charges of sedition and conspiracy to collude with foreign forces, which he denies.

Lai has suffered health problems including diabetes and heart palpitations, and has been ordered to wear a heart monitor during hearings.

In the letter, the signatories call on Türk to demand independent access to all Hong Kong prisons, urge Chinese and Hong Kong authorities to end solitary confinement longer than 15 days, and condemn the use of imprisonment to silence political dissent.

Read the full letter here.