A Polish mayor who was stabbed on stage during the finale of a medical charity event has died, the country's president announced Monday.

Gdnask Mayor Pawel Adamowicz was attacked on stage by a knife-wielding man during the “Lights to Heaven” fundraiser organized by the Great Orchestra of Christmas Charity, one of Poland’s most prominent charities.

"Paweł Adamowicz has gone," Polish President Andrzej Duda tweeted, according to a translation.

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The suspected assailant, who was later arrested and identified by police as a 27-year-old from Gdansk, shouted from the stage that he had been imprisoned by a political group -- to which the mayor formerly belonged -- despite being innocent, according to Polish media.

“Hello! Hello! My name is Stefan, I was jailed but innocent. ... Civic Platform tortured me, that's why Adamowicz just died,” the man reportedly said after stabbing Adamowicz.

Adamowicz underwent five hours of surgery for stab wounds to his heart and abdomen, according to Sky News.

“We couldn't win,” health minister Lukasz Szumowski told reporters.

Adamowciz had been the mayor of Gdansk, a Baltic port city, since 1998. He was part of the democratic opposition born in that city under Lech Walesa’s leadership during the 1980s. He was re-elected to a sixth term as mayor in the fall.

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The Great Orchestra of Christmas Charity raises money for state-of-the-art medical equipment from Poland’s health care system, mostly for children but also for the elderly.

The Associated Press contributed to this report.