Throwing smoke bombs and lighting fires, thousands of angry farmers demonstrated in Warsaw against European Union regulations and cheap Ukraine imports, with police reporting that two officers had been injured and a dozen protesters arrested.

Some demonstrators on Wednesday tried to force their way past security railings onto parliament grounds, according to police. Farmers also organised tractor blockades on roads across the country.

Polish farmers have been blocking border crossings with Ukraine since last month to protest against what they say is unfair competition from goods entering from Ukraine.

In a bid to help Kyiv economically, the EU in 2022 scrapped tariffs on Ukrainian goods transiting the 27-nation bloc by road. But logistical problems mean a lot of the Ukrainian cereal exports destined for non-EU countries have accumulated in Poland, undercutting local producers.

The border blockades and grain dispute have strained ties between the neighbours, even as Poland has shown staunch support since the Russian invasion. Farmers in several other European countries have also been protesting for weeks over these conditions.

Poland’s Prime Minister Donald Tusk said last week the government was mulling a temporary closure of the border with Ukraine for goods. On Monday, he called on the EU to impose full sanctions on food and agricultural imports from Russia and Belarus – a proposal backed by Ukraine.