The step by the communist authorities in 1981 “was the suppression of a social eruption of a craving for freedom,” Andrzej Duda said as he placed a candle at the foot of the Papal Cross monument in the Polish capital’s iconic Piłsudski Square.

Meanwhile, Karol Nawrocki, the head of the Institute for National Remembrance (IPN) – a state body set up to catalogue communist crimes – said: “Today, the torch of freedom also burns. We will not allow the responsibility for national truth to be extinguished.”

Nawrocki is running in next year’s presidential election, backed by the right-wing opposition Law and Justice party.

Poland's last communist ruler, General Wojciech Jaruzelski, imposed martial law, with Moscow's backing, on December 13, 1981, in a bid to crush the first independent trade union behind the Iron Curtain, Solidarity, which threatened communist rule.

Jaruzelski argued that the decision helped avert a Soviet-led military intervention like those that crushed similar protests in Hungary in 1956 and Czechoslovakia in 1968. However, his opponents saw it as a desperate attempt to cling to power.

Under military rule, which lasted until 1983, dozens of demonstrators were killed and thousands more jailed in Poland.

Decades later, on trial for declaring martial law and for human rights violations, Jaruzelski defended his decision by saying it was "evil but it was a far lesser evil than what would have happened without it," adding that he regretted the decision’s "social costs."