He made this statement after voting, Censor.NET reports citing 112 Ukraine TV channel.
According to him, the situation that occurred in Mariupol is unacceptable.
"I believe that the situation in Mariupol is absolutely unacceptable. From the very beginning, I stressed the need to hold elections in Mariupol and the fact that, according to my information, various falsifications were being prepared there, can not be afforded," the president said after voting at a polling station in Kyiv.
Poroshenko said he had already instructed competent law enforcement authorities to investigate the causes obstructing electoral process in Mariupol.
Related materials: Local elections 2015