European Council President Donald Tusk arrived in his native Poland where he has been summoned to give evidence to a secretive investigation. He denounced the “witch-hunt” against him.

As reported by the BBC, the investigation was launched to determine whether two former leaders of the country’s military counter-intelligence service (SKW) exceeded their authority in agreeing to co-operate with a foreign intelligence service in 2010 and 2013.

According to reports, at stake is whether Tusk, who was Poland’s prime minister at the time, authorised this alleged agreement with Russia’s Federal Security Service (FSB).

“I have no doubt that this is part of a political witch-hunt,” Tusk said. Its outcome rested in the “hands of the people”, he added according to the Agence France-Presse (AFP).

The feud between Tusk, who served as Polish prime minister from 2007 to 2014, and the country’s ruling Law and Justice Party (PiS) party has intensified. Tusks’ Civic Platform party is now the main opposition.

Throngs of supporters escorted Tusk from Warsaw’s central railway station to the prosecutor’s office.

PiS leader Jaroslaw Kaczynski holds Tusk politically responsible for the 2010 plane crash in Smolensk, Russia, which killed his twin Lech Kaczynski, as well as 95 others on board.

The government has also accused Tusk of abusing his EU position to meddle in domestic affairs.

Last month, Poland was the only one of 28 EU member states to vote against Tusk’s re-election as president of the European Council.