More than 10 bullets hit the car in Wednesday’s attack near the village of Lesnyky, about five kilometers (three miles) from the capital Kiev, according to a police statement.
The driver of the vehicle was injured in the incident.
The police statement said that a criminal case on suspicion of premeditated murder had been opened.
A senior lawmaker representing the People’s Servant Party of President Volodymyr Zelenskyy said the aide, Serhiy Shefir, was not injured. Shefir, 57, is one of the president’s closest officials and heads a group of advisers.
“I spoke to him briefly, everything is fine, he is alive and well,” said Davyd Arakhamia, quoted by the Russian news agency RIA Novosti.
Zelenskyy denounces an act of “weakness”
Zelenskyy, who came to power promising to confront the country’s oligarchs and fight corruption, is currently in the United States to attend the United Nations General Assembly.
He said he did not know who was responsible for the attack, but vowed to continue the planned reforms despite the incident.
This week, the Ukrainian parliament is due to debate a presidential law aimed at reducing the influence of the oligarchs.
“Sending me a message by shooting my friend is a weakness,” Zelenskyy said.
“It does not affect the strength of our team, the path I have chosen with my team – to change, to clean up our economy, to fight crime and the big influential financial groups.
“It doesn’t affect that. On the contrary, because the Ukrainian people gave me a mandate for change.
Interfax Ukraine quoted Zelenskyy’s adviser Mykhailo Podolyak Podolyak as saying: “We of course associate this attack with an aggressive and even militant campaign against the head of state’s active policies.
Podolyak told Reuters that “the overt, deliberate and extremely violent assault with automatic weapons cannot be characterized any differently than the attempted murder of a key member of the team.”
Kremlin denies any involvement
Oleksandr Korniienko, the leader of Zelenskyy’s political party, has suggested possible Russian involvement in the attack.
“A Russian trace should not be absolutely excluded. We know their ability to organize terrorist attacks in different countries, ”Korniienko told reporters.
Kremlin spokesman Dmitry Peskov said the assessment had “nothing to do with reality”.
Tensions between Kiev and Moscow have intensified in recent years following Russia’s annexation of the Crimean peninsula in early 2014 and the Kremlin’s support for separatist forces fighting Ukrainian troops in the Donbass.
Rebels seized part of the region’s territory in April 2014, weeks after Moscow seized the Crimean peninsula from the Black Sea.