Poland’s prime minister, Donald Tusk, has vowed to see through a contested overhaul of the country’s constitutional court, declaring that “in certain matters, there can be no compromise”.

In a prime-time television address on Saturday night, Tusk was defiant, despite overnight protests that saw riot police drafted to protect the court’s building, saying the shake-up was vital to restore a tribunal crippled by years of political disputes.

Paralysed for more than a decade, the court sat at the core of rule of law clashes between the rightwing Law and Justice (PiS) party and the EU during the party’s eight-year rule.

Since returning to office in 2023, the centre-right Tusk has sought to unwind those judicial changes, but his agenda has been frustrated by opposition-aligned presidents with extensive veto powers. Earlier this year, president Karol Nawrocki refused to swear in five judges approved by parliament.

The crisis flared again on Friday when a group of government-backed judges attempted to seize procedural control of the tribunal, suspending the PiS-appointed chief judge and deputy and prompting street protests.

Defending the action, Tusk said “there was never any doubt that the court in the form imposed by PiS was not a genuine court”, citing adverse rulings from European tribunals.

He compared the opposition outrage to “a thief snatching an elderly woman’s handbag, running off, and when he is caught, he screams that he is subjected to violence”.

Tusk said: “Let’s call things for what they are: for years, there have been organisations and politicians in Poland who seek to destroy democracy and the rule of law. It is no coincidence they find support among pro-Russian forces globally.”

He later highlighted that Russia’s former president Dmitry Medvedev had joined the opposition in an outcry over the changes, accusing Warsaw of “a constitutional coup” and “hounding the conservatives”. “And everything is clear,” Tusk said.

He also criticised opposition-aligned Nawrocki for joining the protests on Friday night and forcing his entry into the court’s building to intervene. “In a democratic state, no politician can enter a court to issue orders or intimidate judges – not even the president,” Tusk said. “We Poles have succeeded too well in building a strong state to surrender now.”

He said it was the government’s duty to ensure its security and the conditions necessary for the court to operate. “And I intend to fulfil that duty,” he said.

The confrontation sets the battle lines before next year’s parliamentary election, with polls pointing to a close race between Tusk’s broad coalition and the nationalist right.

However, experts remain divided over whether the government’s procedural gambit at the court is lawful.

Poland’s Helsinki Foundation for Human Rights said on Saturday the legal basis for the temporary suspension was “questionable”, warning it would “not contribute” to restoring the court.

The foreign minister, Radosław Sikorski, conceded that the events outside the court were “not elegant”, but insisted: “The alternative was to concede an unconstitutional transformation of Poland into a presidential republic.”

Nawrocki held some cross-party political talks on Saturday, with no apparent breakthrough. His senior aide, Zbigniew Bogucki, responded to Tusk’s address, calling the prime minister “a pathological liar, who is setting Poland ablaze”.