Tens of thousands of farmers and their supporters warned on Wednesday they would bring Poland to a standstill, after violent clashes with police outside the country’s parliament in Warsaw.

The protesters had gathered at the prime minister’s office in the Polish capital, burning tyres and throwing firecrackers as they demanded a halt to cheap imports and environmental regulations they say harm their livelihoods.

They then marched towards parliament, where a Reuters witness saw police using batons, pepper spray, tear gas and stun grenades against demonstrators, while some protesters hurled rocks, cobblestones and firecrackers at the security forces.

“Due to physical aggression against police officers by some of the people protesting … it was necessary to use direct coercive measures,” Warsaw police wrote in a post on X.

Poland’s Interior Minister Marcin Kierwinski said in a post on X that “23 provocateurs have been detained”. Local media footage showed several protesters forcing their way onto parliamentary grounds, before being subdued by police.

Tomasz Obszanski, a farmers’ union leader and protest organiser, told Reuters that police began blocking protesters from leaving as the demonstration ended.

“Everything was peaceful, and suddenly the police came out of nowhere, there were loud bangs, the police started using (tear) gas and simply provoking people leaving the protest,” said Obszanski, leader of the NSZZ RI Solidarnosc union for individual farmers.

Farmers across the European Union have been calling for changes to restrictions placed on them by the bloc’s Green Deal plan to tackle climate change, and for the re-imposition of customs duties on imports of agricultural products from Ukraine that were waived after Russia’s invasion.

Obszanski said that the farmers were leaving Warsaw empty-handed after their request to meet with Polish Prime Minister Donald Tusk was turned down and warned of further measures.

“After what happened today, there will be a blockade of the entire country … Poland will come to a standstill, because a Polish farmer will not allow himself to be treated in such a way, to be batonned,” Obszanski said.

Tusk has invited farmers leaders for talks on Saturday.

Obszanski estimated the number of protesters was in the high tens of thousands, while Warsaw city officials said they numbered about 30,000.

The farmers, who were making good on their promise to return to Warsaw after thousands of them marched through the city a week earlier, have been backed by Poland’s biggest labour union, NSZZ Solidarnosc, as well as hunters and forestry workers.

Earlier some protesters burned a coffin bearing a sign that read “farmer, lived 20 years, killed by the Green Deal” in the street in front of Tusk’s office, blowing horns and holding Polish flags aloft before marching on parliament.

Television footage showed tractors on the outskirts of Warsaw being stopped from entering, while farmers blocked roads elsewhere in the country.

Tusk faces a delicate balancing act, seeking to address farmers’ concerns while also maintaining his staunch support for Kyiv in a year when it faces both local and European elections.

He has said that market disruptions were not only caused by imports from Ukraine, but also from Russia and its ally Belarus, and on Monday said Poland planned to ask the EU to ban imports of Russian and Belarusian agricultural products.