Armed riot police and water cannon were deployed in cities across Belarus and the internet was shut down across the country on a day of protest and human rights marches.

People were on Saturday night reported to be still attempting to demonstrate in the capital, Minsk, as well as in Brest and Grodno, on what was the national Freedom Day. There were sporadic outbreaks of violence as masked police closed down key roads and charged at marchers to stop crowds forming. Witnesses claimed it was the most determined crackdown by President Alexander Lukashenko so far in what has been two months of protests and opposition to his 23-year rule.

A cordon of riot police armed with clubs laid into one group trying to march down a main avenue, said one activist, Alexander Ponomarev: “They’re beating the participants, dragging women by the hair.”

Opposition leader and former presidential candidate Vladimir Nekliayev is among more than 300 people who have been arrested and detained over the past few days, while 57 people using a human rights and legal centre in Minsk were held for several hours before being released.

“Lukashenko is in a panic, in fear of his own people,” said Natalia Kaliada, of the charity Belarus Free Theatre, who spoke from Brussels, where she had been lobbying the EU to resume sanctions against the regime in Belarus that were lifted last year.

“It’s a strategy of arrests and clearing the streets and blocking the internet that they think will spook people, but people are very angry. All these arrests and splitting up the crowds might make things a little quieter in Minsk, but now these protests are happening all over Belarus,” she said. “This is the worst crackdown over the last seven years, but it would have been the biggest protest. People don’t care, they want an end to this dictator. They say ‘basta’ – enough.”

The European Union lifted most of the sanctions against named individuals in Belarus’s ruling elite in February 2016 in what was seen by some critics as being a reward for the role Belarus took in hosting peace conferences between Russia and Ukraine. The move horrified many human rights organisations, which point to the deeply repressive regime led by Lukashenko, who was described by former US president George W Bush’s secretary of state as “Europe’s last dictator”.

“It is a geopolitical game, Belarus is barely on the radar for the EU and yet it is dangerous to ignore what is happening there – not just dangerous for people in Belarus, Russia and Ukraine, but for the whole world,” said Kaliada.

The most recent unrest has been sparked by a presidential decree that taxes the unemployed and part-time workers around £200 a year. The decree, launched as an “anti-parasite” tax, met widespread criticism from citizens, activists and journalists.

Earlier this month Lukashenko announced that he would suspend the deadline for payment until his government had reviewed the policy, but protest against his Soviet-style rule has continued to grow. Last week the president claimed that foreign-supported elements were agitating to bring him down.