More than 1,000 opposition supporters protested outside Macedonia's parliament on May 6 over the 2011 police killing of a student, a day after violence at a similar demonstration left 38 officers and one protester injured.
Protesters peacefully chanted slogans calling for the resignation of conservative Prime Minister Nikola Gruevski's government, which a left-wing opposition party has accused of trying to cover up the killing.
Interior Minister Gordana Jankulovska said six of the officers injured May 5 were hospitalized in severe condition.
She said that protesters used metal bars to beat police and threw stones, bottles, and eggs in what she called a "brutal attack."
Social Democrat Zoran Zaev, Macedonia's opposition leader, accused Prime Minister Nikola Gruevski of attempting to cover up the death of Martin Neskoski, who died after being beaten up by police while celebrating Gruevski's election win.
Zaev released audio recordings in which he said the prime minister and other officials discuss how to cover up the killing.
Government officials called the charges "absurd."