Pawel Adamowicz, the mayor of the Polish city of Gdansk, who was a victim of a knife attack, succumbed to his wounds on Monday, Polish Radio broadcaster reported.

Following the attack, the mayor was taken to a hospital, where he underwent a five-hour-long surgery. Polish President Andrzej Duda said later that he received information, the doctors had managed to restore Adamowicz's heartbeat.

Z niedowierzaniem przyjęliśmy informację o tragicznej śmierci Prezydenta @gdansk @AdamowiczPawel. Był niezwykle sympatycznym i inteligentnym człowiekiem, przyjacielem Gminy Władysławowo. Na zawsze dla nas takim pozostanie. Rodzinie i bliskim składamy najszczersze kondolencje. pic.twitter.com/FeZ814wzid — Gmina Władysławowo (@wladyslawowopl) 14 января 2019 г.

The suspect, a 27-year-old man, left prison last month after having served a 5.5-year-long term for bank robbery. He is set to undergo a psychiatric examination, prosecutor Krzysztof Sierak told reporters earlier on Monday.

"We believe his mental stability raises doubts. Two psychiatrists will examine him", Sierak said.

He specified that the Gdansk regional prosecutor had already launched an investigation into the assassination attempt. The suspect's blood was tested for alcohol and psychotropic drugs, but the prosecution has not received the results of the analysis yet.

A representative from the Polish penitentiary service has told Sputnik that the suspect had mental health problems that were detected while he was serving his prison term.

"During his prison term, closer to its end, a psychiatrist examined this person. It was detected that he was in remission of a serious [mental] disorder… This did not impede him from serving his term to the end", the representative said.

The attacker's motives have not been officially revealed yet.

The Warsaw authorities have decided to declare a three-day mourning following the mayor's death.

"Today, when we still had hope that a miracle would happen and that the mayor will survive, I asked for a meeting of representatives of the political forces. I hoped that we would go together in a march against violence in Gdansk… We decided that we would not organize marches, but if possible, we will come to the funeral and there we will give honor to the mayor Adamowicz… We decided that it [day of mourning] will be the day the family will choose as the day of the funeral," Polish President Andrzej Duda said.

Duda said during a briefing after consultations with the country's political forces that he hoped to organize a march against violence in Gdansk, but after Adamowicz died, he decided that a one-day country-wide mourning will be declared on the day of Adamowicz's funeral, the date of which is not yet determined.