Egyptian police violently disbanded a small protest mounted Tuesday night by activists calling for democracy in central Cairo, arresting dozens of some of the country's best-known rights advocates just two days after the military-appointed interim president signed an acutely restrictive law regulating demonstrations in the turbulent country.

Security forces wielding fire hoses and tear-gas launchers charged a group of more than 100 demonstrators protesting a constitutional article granting the army authority to try civilians in military courts, chasing them onto side streets and detaining up to 70, rights groups said.

The dispersal kicked off clashes between protesters and police in the streets around Cairo's Tahrir Square, with police firing tear gas and protesters answering with rocks and burning tires. It marked the most direct assault by security forces on the Tahrir Square revolutionary activists — who oppose both the military and the Muslim Brotherhood — since an army coup ousted Islamist President Mohammed Morsi in July.

At least 13 of the 50 representatives on the committee writing Egypt's new constitution said they were freezing their memberships until the detainees, including the high-profile activist and co-founder of the No Military Trials rights group, Mona Seif, were released, state media reported.

Police acted under a law enacted by the military-backed government this week that severely curtails the rights of citizens to peacefully assemble — and grants security forces broad authority to quash demonstrations, including with both riot control weapons and live ammunition.