Protests have turned violent in Kiev, Ukraine after President Viktor Yanukovych signed into law a bill that curbs anti-government protests. Reuters reports up to 100,000 Ukranians gathered around Kiev’s Independence Square on Sunday in blatant defiance of the laws.

Reports say masked demonstrators attacked police and tried to overturn a bus after opposition politicians called on protesters to ignore the new laws. Opposition leaders however pleaded with protesters not to justify a police crackdown.

Police used water cannons to break up demonstrations outside the Parliament building, while protesters threw smoke bombs and fireworks. The interior ministry says 30 police were hurt, including at least 10 who required hospitalization.

Protesters were originally camped out in opposition to President Viktor Yanukovych’s rejection of an European Union partnership deal. The protests later grew to include grievances over what they said is government corruption and abuse.

The anti-protest laws make much of those protest activities illegal. They ban unauthorized installation of tents, stages or loudspeakers in public, mandate jail sentences for participating in “mass disorder” and wearing face masks and helmets, reports Reuters.

Critics include the U.S. State Department, who call the laws undemocratic. U.S. Secretary of State John Kerry said the laws “violate all of the norms of the OSCE (Organization for Security and Co-operation in Europe) and the EU.”

Yanukovych loyalists have also called for the establishment of a people’s assembly and a new Constitution. A spokeswoman for opposition politican Vitaly Klitschko says President Yanukovych agreed to meet with him, but Yanukovych’s camp has not confirmed.