China has deployed a fresh contingent of troops into its military base in Hong Kong amid the territory’s worst political crisis since returning to Chinese rule in 1997.

State-run Xinhua news agency described Thursday’s deployment as a routine rotation of personnel and equipment into the People Liberation Army’s garrison in the financial hub. State television aired footage of armored personnel carriers and trucks entering the garrison after crossing the border from the neighboring city of Shenzhen.

Hong Kong has been gripped by nearly three months of heated and often violent protests that began as demonstrations against a controversial extradition bill, but have since evolved into calls for greater democracy and an independent probe into allegations of police brutality.

The city’s police force Thursday refused to grant permission to the activist group Civil Human Rights Front to stage another mass rally on Saturday, citing violent clashes between riot police and demonstrators during last weekend’s demonstrations. Police used tear gas and water cannons against demonstrators who broke away from a larger group of peaceful marchers. Some of the protesters threw bricks at police, attacked them with sticks and rods and sprayed detergent on streets to make it slippery for police.

Saturday’s planned demonstrations would mark five years since Beijing’s rejection of universal suffrage for Hong Kong. Pro-democracy activists fear that China is steadily eroding the basic freedoms they have enjoyed since the 1997 handover from British rule.