The border with Belarus has become a security flashpoint, with thousands of migrants and refugees, mostly from the Middle East, crossing it into Europe.

Mr Tusk has dubbed this a “hybrid war of migration” facilitated by Alexander Lukashenko, the president of Belarus.

“Those are not refugees, those are less and less migrants, families, poor people needing help,” Mr Tusk added. “In 80 per cent of the cases, these are organised groups of men, aged 18 to 30, very aggressive.”

As the weather warms, Poland is seeing an increase in crossings, up to 200-300 a day in May. Poland was part of the Soviet-led Warsaw Pact during the Cold War but joined Nato after Communism fell in the 1990s.