Macedonian police have arrested about 30 people, including two opposition MPs, former senior police officials and an ex-minister, over an April attack on parliament in which scores of people were injured.
Around 100 nationalist demonstrators, including masked men, stormed the assembly in Skopje on April 27, attacking MPs in protest over the vote for a new parliamentary speaker.
Several MPs were beaten in the rioting, including the leader of Social Democrats, Zoran Zaev, who has since become prime minister.
The public prosecutor's office for organized crime and corruption said in a statement on Tuesday it had ordered an investigation into 36 people suspected of "terrorist endangerment of the constitutional order and security".
Police said around 30 people were arrested including former interior minister Mitko Cavkov and two MPs from the conservative VMRO-DPMNE party.
They were to be brought before a judge later in the day, when supporters of the VMRO-DPMNE were due to hold a protest against the detentions.
The violence followed months of protests by nationalists opposed to a coalition deal between Zaev's Social Democrats and minority ethnic Albanian parties, which they alleged was a threat to national unity.
Ethnic Albanians make up around a quarter of Macedonia's two million people.
The storming of parliament, which met with international condemnation, erupted over the election of Talat Xhaferi, who is ethnic Albanian, as speaker.
The protesters alleged the vote was illegal.
The Social Democrats accused the VMRO-DPMNE party -- in power for a decade until last year, and supported by the nationalists -- of fanning ethnic tensions in a bid to stay in power.
Last month, nationalist Pance Angelov was sentenced to four years in prison for violently pulling the hair of a woman MP during the attack.
In May, nine Macedonians received suspended prison sentences for their part in the violence.