Police in Belarus arrested hundreds of people who took to the streets on Sunday chanting “I’m going out”, the last known written words of an anti-government protester who died last week, a prominent human rights group said.

A witness in the capital Minsk said police arrested several dozen people and used tear gas, rubber bullets and stun grenades to disperse the crowds demonstrating against President Alexander Lukashenko.

Belarus is in political crisis as tens of thousands of people have taken to the streets each week since an election in August, calling for Lukashenko to resign after 26 years in power. Lukashenko has rejected Opposition accusations that the election was rigged in his favour.

The street rallies were re-ignited following the death of Roman Bondarenko, a 31-year old anti-government protester. He died in hospital in Minsk on Thursday following what demonstrators said was a severe beating by security forces.

The interior ministry has denied responsibility for Bondarenko’s death, saying he was killed in a scuffle with civilians.

The protesters took to the streets in many cities across Belarus, including Brest and Minsk.

Security forces in riot gear and shields on Sunday flooded the square where Bondarenko was detained, pulling down Opposition flags, kicking over memorial lamps and dragging people from the crowds and frog-marching them to vans, a witness said.

Video footage by local media also showed security forces entering apartments in the area in search of protesters. A video clip posted on social media showed three men in riot gear attending to a man who appeared to be unconscious.

Viasna (Spring) human rights group said 504 people had been detained by the police during Sunday’s protests across the country so far.