The day before, demonstrators protested in front of the presidential palace in Warsaw and other Polish cities against the amendments to the country's judicial system.
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At some point, some protesters used tear gas against riot police which responded in kind, the broadcaster reported.
There is no information on the detained protesters yet, the media added.
Poland's long-disputed supreme court legislation, which, among other things, lowered the retirement age of Supreme Court judges from 70 to 65 and could potentially lead to the retirement of 27 out of 72 judges, entered into force on July 4. The changes are suspected to grant political authorities control over the judiciary and thus go against EU law.