UN human rights experts have told China a new security law for Hong Kong poses a serious risk to the city’s freedoms.
The legislation has been widely criticised since it was imposed by Beijing in June after months of huge pro-democracy protests in Hong Kong last year.
In the letter made public on Friday, experts said the law breached international legal obligations.
They also voiced concerns it could be used to prosecute political activists.
The law, which criminalises secession, subversion, and collusion with foreign forces, has silenced many protesters since it came into effect.
Last month Hong Kong police arrested 10 people in their largest operation yet under the legislation.
It centred on a dramatic raid of the city’s biggest pro-democracy newspaper, Apple Daily, and the arrest of its founder Jimmy Lai.