A Moscow court has sentenced Alexei Navalny to two years and eight months in a prison colony in a landmark decision for Vladimir Putin’s crackdown on the country’s leading opposition figure.

The move triggered marches in Moscow and the arrest of more than 1,000 protesters.

Navalny, who has accused the Russian president and his allies of stealing billions, was jailed for violating parole from a 2014 sentence for embezzlement in a case he has said was politically motivated.

After the verdict, several hundred Navalny supporters marched in central Moscow. Videos by local media or shared on social media showed police in body armor hitting protesters with staves. More than 1,000 people were arrested across the country in the course of the day, according to the independent monitoring group OVD-info.

The court’s decision makes Navalny the most prominent political prisoner in Russia and may be the most important verdict against a foe of Putin’s since the 2005 jailing of the oligarch Mikhail Khodorkovsky.

Ahead of the verdict, Navalny looked across the court room to his wife Yulia, and traced a heart on the glass around the dock.