The UN commissioner, Michelle Bachelet, wrote in an opinion piece Saturday in the South China Morning Post that Hong Kong leader Carrie Lam's government must prioritize "meaningful, inclusive" dialogue to resolve the crisis.
She urged Lam to hold an "independent and impartial judge-led investigation" into police conduct of protests. It has been one of key demands of pro-democracy demonstrations that have roiled the territory since June.
China's UN mission in Geneva said that Bachelet's article interferes in the internal affairs of China and exerts pressure on the city's government and police, which "will only embolden the rioters to conduct more severe radical violence."
It said Bachelet made "inappropriate comments" on the situation in Hong Kong and that the Chinese side had lodged a strong protest in response.
Since the unrest broke, protesters have disrupted traffic, smashed public facilities and pro-China shops, and hurled gasoline bombs in pitched battles with riot police who have responded with volleys of tear gas and water cannons.
The occupation of several universities by protesters earlier this month after fiery clashes with police capped one of the most violent chapters in the turmoil, which has contributed to the city's first recession in a decade.
Lam appealed for the current calm to continue but has refused to bow to protesters' demands, which include free elections for her post and the legislature as well as an independent probe into police conduct.
Hong Kong police have arrested 5,890 people as a result of the protests.
On Saturday, hundreds of silver-haired activists joined young protesters for a unity rally, vowing that their movement will not fade away until there is greater democracy.
The rally at a park downtown was among several peaceful gatherings by protesters this week to keep up pressure on the government following a local election victory by the pro-democracy bloc and the gaining of US support for their cause.
"The government is still stubborn. Every one of us, young and old, must contribute in our own way. The movement will not stop," said a 63-year-old woman who identified herself as Mrs. Tam.
Some protesters returned to the streets Saturday night, using metal fences, cartons and bricks to block traffic in the Mong Kok area in Kowloon. Dozens had gathered there to mark three months since police stormed a subway car in the area and hit passengers with batons and pepper spray. Most left after police reportedly fired pepper balls and issued warnings.
More rallies are planned Sunday, including an anti-tear gas protest and a gratitude march to the US Consulate. (AP)