KYIV -Ukrainian police opened an investigation on Friday after a young lawmaker fell ill and died in a taxi in the capital Kyiv following what prosecutors said was a heart attack.
However, the head of Kyiv's police said it was most likely that Anton Poliakov, 33, had died of natural causes.
Poliakov belonged to the "For the Future" party, having defected from President Volodymyr Zelenskiy's ruling "Servant of the People" party over policy disagreements.
"For the Future", which has 22 lawmakers, is associated in the Ukrainian media with Ihor Kolomoisky, one of the country's richest men, though Kolomoisky has not publicly associated himself with the party.
The General Prosecutor's Office said Poliakov had been found unconscious in the back seat of a taxi after it was stopped by police for a traffic offence.
The driver said the passenger had got in near a public transport stop outside the city centre and then complained of feeling sick, the prosecutors' statement said.
Kyiv police head Ivan Vyhovsky told a briefing that Poliakov had been to a restaurant, and had drunk alcohol.
After that, he and another man drove around the city for about an hour and a half. He then got into the taxi, where he later died.
Vyhovsky said Poliakov had not gone home as he had had a row with his partner, also a lawmaker who left Zelenskiy's party. Her office declined to comment.
"We cannot say 100% that it was natural death, but we are inclined to believe that it was a natural death," Vyhovsky said.
Poliakov had been attacked by an unknown person in September 2020, and required medical attention, according to a police statement at the time.
After leaving Zelenskiy's party, Poliakov was one of a group of lawmakers who submitted more than 16,000 amendments in an unsuccessful bid to derail a banking bill seen as unfavourable to Kolomoisky.
The tycoon denied asking for the amendments, but said the bill was against Ukraine's interests.
Poliakov sat on parliament's anti-corruption committee. Graft is one of Ukraine's biggest problems, and an obstacle to its bid to join the European Union and NATO.