Belarusian president Alexander Lukashenko has warned that his security forces will take “the most severe” action against any unrest, as the country braces for potentially its biggest anti-government protest in years.

Rights groups say Belarusian police and its KGB security service have arrested, fined or taken other action against almost 300 protesters amid a wave of demonstrations leading up to Saturday’s planned rally in the capital, Minsk.

Mr Lukashenko (62) – who has ruled Belarus since 1994 – said this week that the KGB had arrested militants who trained in Ukraine and received funding from neighbouring EU members Poland and Lithuania. Kiev dismissed the claim and critics accused the authoritarian leader of trying to discredit the protest movement.

“We are capable today of preserving peace and quiet in our country, and we are not scared of anyone,” Mr Lukashenko told officials ahead of Saturday’s march. “We won’t shut anyone’s mouth, but a step to the left or a step to the right away from the law will be stopped in the most severe manner.”

Belarusian state media reported that 26 people had been arrested in recent days during searches that uncovered guns, grenades, knives, axes, bulletproof vests and various insignia including those of radical Ukrainian organisations.

Earlier this week, Mr Lukashenko accused a “fifth column” in Belarus of wanting to “blow up the situation in the country”.

“We already arrested a few dozen . . . who trained in camps with weapons. One of the camps was in the [Belarusian] region of Bobruisk-Osipovich. The other camps were in Ukraine . . . The money came here through Poland and Lithuania.”

The Ukrainian foreign ministry denied the claims, calling them “provocative and damaging to the development of neighbourly relations” between the countries.

Repression of opponents

While promising a continuation of Soviet-era certainties, Mr Lukashenko warns of the danger of reform by pointing to upheaval in Ukraine and other ex-Soviet states where protesters have demanded greater freedom and democracy.

The former collective farm boss has long sought to balance Belarus’s relations between Russia and the European Union, while always moving back towards Moscow when domestic or foreign criticism of his rule grew too loud for comfort.

Mr Lukashenko appears to have been unnerved by Russia’s aggression in Ukraine, however, and he has not recognised its annexation of Crimea.

Belarus refused to pay the gas price demanded by Russia last year, and has racked up a debt to Moscow of some $600 million (€555 million) Russia subsequently cut oil supply to its neighbour and re-imposed border controls after Belarus introduced visa-free entry for short-term visitors from the EU, United States and other countries.

The latest protests were triggered by Mr Lukashenko’s announcement of an annual “social parasite tax” of $250 (€231) on people who are unemployed or work irregularly, which compounded widespread anger over deepening poverty and lack of opportunity among Belarus’s 10 million people.