The call center of Ukrainian presidential candidate Volodymyr Zelensky's campaign staff has already received more than 1,500 reports about irregularities.

"Most of them deal with organization-related irregularities, but signals that results are being distorted have already begun arriving. They deal with some unclear 'arrivals' [of groups of voters], some people standing at polling stations' exists," ZE!Team coordinator Oleksandr Korniyenko said at a press briefing on Sunday.

The largest number of violations is linked with the presence of the names of dead people on voters' lists, he said. For instance, a person who died in 1995 has been registered to vote.

Violations have also been committed against ZE!Team observers, he said.

"They are demanding that our monitors remove their badges. They are calling it canvassing. But it is not canvassing. We have every reason in accordance with the law to think so. And we stand ready to defend it in courts," Korniyenko said.

Ukraine is holding the first round of its presidential election on Sunday. The polling stations will close at 20:00. A record-large number of candidates - 39 - are running in this presidential election.