Poland's ruling Law and Justice party leader Jaroslaw Kaczynski has blamed European Council President Donald Tusk for Britain's vote to leave the EU, and called for him to disappear from European politics.
Mr Kaczynski told local media: "A particularly dark role was played by Donald Tusk, who conducted negotiations with the British and in fact contributed to them getting nothing.
"Hence, he is directly responsible for Brexit and should simply disappear from European politics. But this concerns the whole of European Commission in its present composition."
Donald Tusk, the president of the European Council, said Brexit was an "historic moment" but "not a moment for hysterical reactions".
He said the EU was prepared for this "dramatic scenario".
Mr Tusk added: "We are determined to keep our unity as 27."
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The incoming president of the European Council, Donald Tusk, has pledged to address the concerns of Britain in his new role.
He said the EU and he personally would take on the concerns voiced by Britain about the EU. "No reasonable person can imagine the EU without the UK," he said.
Prime Minister David Cameron has promised a referendum on continued EU membership by 2017.
Poland's prime minister Donald Tusk has been chosen by European Union leaders to become the new president of the European Council.
The top official will chair EU summits and mediate between the 28 governments for the next two-and-a-half years.
Federica Mogherini, the Italian foreign minister, has also replaced Catherine Ashton as the EU's foreign policy chief.
The Polish prime minister has told David Cameron that governments "cannot stigmatise any national group and must respect European law".
Donald Tusk's office described a phone conversation between the pair this afternoon as "an open and frank exchange of views".
It said Mr Cameron explained he had not intended to stigmatise Polish people who work in the UK when he made comments about child benefits payments to migrants.
But Mr Tusk was said to have told the Prime Minister that Poland could not accept such statements, regardless of their original intentions.
David Cameron and the Polish prime minister have agreed to hold further discussions on the impact of EU free movement on child benefit payments.
The Prime Minister called Donald Tusk this afternoon "to discuss co-operation on a range of bilateral and EU issues", Downing Street said:
The Prime Minister made clear his long-standing view, reiterated in recent days, that the lack of transitional controls for new EU member states in 2004 was the wrong approach and had put pressure on local communities; and that we need to address the impact on countries’ benefits systems, including for example paying child benefit to families living abroad.