An assailant shot dead an assistant to a lawmaker from Poland's main opposition party on Tuesday in an attack its leader Jaroslaw Kaczynski blamed on a "hate campaign" started by Prime Minister Donald Tusk.
Polish media said the attacker had burst into the office of the conservative-nationalist Law and Justice (PiS) party in the central city of Lodz shouting "Kill Kaczynski!"
Police took the attacker, a 62-year old male, into custody after he shot one PiS worker and badly wounded another with a knife.
"It looks like the assailant had both a gun and a knife. He fired several shots," said police spokeswoman Magdalena Zielinska, adding it was too early to speak of his motives.
Kaczynski, the identical twin brother of Poland's late president Lech Kaczynski who died in a plane crash in April, said Tusk's government and anti-PiS media bore responsibility for the attack.
"What has happened is a result of the hate campaign that has been waged against PiS for some time now," he said, accusing Tusk of starting it.
"Today the government is fully responsible for the security of all our offices and all our workers. If anybody says one more word of hatred toward us, this would amount to a call for killing," Kaczynski added.
Tusk expressed his sympathy to the families of the victims in Lodz and urged all politicians to avoid inflamatory talk.
'Cool the temperature'
"In free, democratic Poland, we have never seen political assassinations. This case was apparently politically motivated and we must all first and foremost keep our emotions in check," Tusk told a news conference.
"We must show in the coming weeks and months that this is a one-off. We must all cool the temperature of political rows."
Poland holds municipal polls next month and a parliamentary election next year that Tusk's party is expected to win.
Kaczynski, 61, has abandoned all rhetorical restraint toward his political opponents since losing a presidential election in the summer to the candidate of Tusk's ruling center-right Civic Platform (PO), Bronislaw Komorowski.
Clearly devastated by his brother's death in the crash in Russia that also killed 95 other mostly senior Polish officials, Kaczynski has accused the Tusk government and Moscow of effectively working together to engineer the disaster.
Kaczynski has also refused to have any direct contact with Tusk or President Komorowski in a move political analysts say will erode support for his party among many moderate Poles ahead of next year's parliamentary election.
But Kaczynski's uncompromising stance on issues ranging from relations with Russia to in vitro fertilization, which he opposes, has buttressed support among his core voters, who are mostly older, patriotic-minded, staunchly Roman Catholic Poles.