The former speaker of the Ukrainian parliament Andriy Parubiy has been shot dead in the western city of Lviv, officials have said.
Unverified footage, purportedly of the shooting, appears to show a gunman dressed as a courier approaching Parubiy on the street and holding up a weapon as he walks behind him, before fleeing. A huge manhunt is now under way for the suspect.
Ukrainian President Volodymyr Zelensky described Saturday's attack as a terrible murder and offered condolences to Parubiy's family.
Parubiy, 54, rose to prominence during Ukraine's Euromaidan mass protests, which advocated closer ties with the EU and brought down pro-Russian former President Viktor Yanukovych in 2014.
A special operation, codenamed Siren, has now been launched by Ukrainian authorities aimed at tracking down and arresting the suspected shooter.
All necessary forces and means are being deployed, Zelensky said in a statement.
Ukraine's prosecutors said an unidentified gunman fired several shots at the politician and that Parubiy died on the spot.
Lviv police chief Oleksandr Shliakhovskyi stated that about eight shots were fired from a firearm, which has not yet been identified. The attack appeared to have been very carefully planned.
Meanwhile, Lviv's chief prosecutor Mykola Meret said all possible motives for the shooting were being investigated, including potential Russian involvement.
Sources in Ukraine's law enforcement agencies told BBC News earlier that seven shell casings were later found at the scene. The source also said the attacker was dressed to look like a courier for delivery company Glovo.
A spokeswoman for Glovo expressed that the firm was deeply shocked by the brutal crime and assured full cooperation with the investigation.
Parubiy was a pivotal figure in the Euromaidan movement, organizing and coordinating the armed teams of protesters that defended the camp in Kyiv. He later became secretary of Ukraine's National Security and Defence Council during pivotal moments in Ukraine's struggle against Russian aggression.
Ukraine's Foreign Minister Andrii Sybiha described Parubiy as a patriot and statesman who made an enormous contribution to the defense of Ukraine's freedom, independence, and sovereignty.
Former President Petro Poroshenko called the killing a shot fired at the heart of Ukraine and acknowledged Parubiy's significant contributions to building the Ukrainian army.