Thousands of demonstrators took to the streets of Polish cities Wednesday, some of them hurling stones at police, in protest
at an international copyright treaty criticized as a clampdown on freedom of speech on the internet.

In the city of Kielce around 700 people protested. Some of them threw bottles and stones at police, damaged cars and partially blocked traffic, Polish media reported. Police arrested 24 people. One police officer was taken to hospital for treatment.

In the largest demonstration, in Cracow, 15,000 people took to the streets in a largely peaceful protest.

Demonstrators chanted "Down with censorship" while some had a piece of tape inscribed with "ACTA" glued over their lips.

ACTA is the acronym for the international Anti-Counterfeiting Trade Agreement, which Poland was to sign in Tokyo on Thursday.

Opponents of the treaty, which aims to protect international intellectual property rights and fight online piracy, launched a string of attacks on Polish government websites earlier this week, jamming the websites of the Polish parliament, the prime minister’s office and the Ministry of Culture.