Supporters and opponents of Ukraine's President Petro Poroshenko scuffle during his pre-election campaigning speech in Kiev, Ukraine, Sunday, March 17, 2019. Ukraine will vote for the President on March 31. (AP Photo/Serhii Nuzhnenko)

Ukrainian President Petro Poroshenko greets his supporters during his mass campaigning rally in Kiev on March 17, 2019. - Ukrainian presidential elections will be held on March 31. (Photo by Sergei SUPINSKY / AFP)

Ukrainian President Petro Poroshenko greets his supporters during his mass campaigning rally in Kiev on March 17, 2019. - Ukrainian presidential elections will be held on March 31. (Photo by Sergei SUPINSKY / AFP)

Ukrainian President Petro Poroshenko greets his supporters during his mass campaigning rally in Kiev on March 17, 2019. - Ukrainian presidential elections will be held on March 31. (Photo by Sergei SUPINSKY / AFP)

Opposition activists hold placards and argue with opponents as they protest during a presidential election campaign meeting of President Petro Poroshenko, on March 17, 2019 in Kiev. (Photo by Genya SAVILOV / AFP)

Opposition activists hold placards and argue with opponents as they protest during a presidential election campaign meeting of President Petro Poroshenko, on March 17, 2019 in Kiev. (Photo by Genya SAVILOV / AFP)

Ukrainian President Petro Poroshenko (L) delivers a speech to supporters during a campaign rally in Kiev on March 17, 2019. - Ukrainian presidential elections will be held on March 31. (Photo by Sergei SUPINSKY / AFP)

Ukrainian President Petro Poroshenko delivers a speech to supporters during a campaign rally in Kiev on March 17, 2019. - Ukrainian presidential elections will be held on March 31. (Photo by Sergei SUPINSKY / AFP)

Ukrainian President Petro Poroshenko (C) delivers a speech to supporters during a campaign rally in Kiev on March 17, 2019. - Ukrainian presidential elections will be held on March 31. (Photo by Sergei SUPINSKY / AFP)

Ukrainian President Petro Poroshenko thumbs up as he delivers a speech to supporters during a campaign rally in Kiev on March 17, 2019. - Ukrainian presidential elections will be held on March 31. (Photo by Sergei SUPINSKY / AFP)

Ukrainian President Petro Poroshenko delivers a speech to supporters during a campaign rally in Kiev on March 17, 2019. - Ukrainian presidential elections will be held on March 31. (Photo by Sergei SUPINSKY / AFP)

People listen to the speech of Ukrainian President during a campaign rally in Kiev on March 17, 2019. - Ukrainian presidential elections will be held on March 31. (Photo by Sergei SUPINSKY / AFP)

People listen to the speech of Ukrainian President during a campaign rally in Kiev on March 17, 2019. - Ukrainian presidential elections will be held on March 31. (Photo by Sergei SUPINSKY / AFP)

People listen to the speech of Ukrainian President Petro Poroshenko during a campaign rally in Kiev on March 17, 2019. - Ukrainian presidential elections will be held on March 31. (Photo by Sergei SUPINSKY / AFP)

Ukrainian President Petro Poroshenko (C) delivers a speech to supporters during a campaign rally in Kiev on March 17, 2019. - Ukrainian presidential elections will be held on March 31. (Photo by Sergei SUPINSKY / AFP)

A woman holds a portrait of Ukrainian President Petro Poroshenko while people listen to his speech during a campaign rally in Kiev on March 17, 2019. - Ukrainian presidential elections will be held on March 31. (Photo by Sergei SUPINSKY / AFP)

A man holds a portrait of Ukrainian President Petro Poroshenko while people listen to his speech during a campaign rally in Kiev on March 17, 2019. - Ukrainian presidential elections will be held on March 31. (Photo by Sergei SUPINSKY / AFP)

People listen to the speech of Ukrainian President during a campaign rally in Kiev on March 17, 2019. - Ukrainian presidential elections will be held on March 31. (Photo by Sergei SUPINSKY / AFP)

People listen to the speech of Ukrainian President during a campaign rally in Kiev on March 17, 2019. - Ukrainian presidential elections will be held on March 31. (Photo by Sergei SUPINSKY / AFP)

Thousands of supporters of Ukrainian President Petro Poroshenko attend a campaign rally in Kiev on March 17, 2019. - Ukraine's Presidential elections will be held on March 31, 2019. (Photo by Sergei SUPINSKY / AFP)

Thousands of supporters of Ukrainian President Petro Poroshenko attend a campaign rally in Kiev on March 17, 2019. - Ukraine's Presidential elections will be held on March 31, 2019. (Photo by Sergei SUPINSKY / AFP)

Ukrainian President Petro Poroshenko greets supporters during a campaign rally in Kiev on March 17, 2019. - Ukraine's Presidential elections will be held on March 31, 2019. (Photo by Sergei SUPINSKY / AFP)

Ukrainian President Petro Poroshenko greets supporters during a campaign rally in Kiev on March 17, 2019. - Ukraine's Presidential elections will be held on March 31, 2019. (Photo by Sergei SUPINSKY / AFP)

Ukrainian President Petro Poroshenko gestures while delivering a speech during a campaign rally in Kiev on March 17, 2019. - Ukraine's Presidential elections will be held on March 31, 2019. (Photo by Sergei SUPINSKY / AFP)

Opposition activists scuffle with supporters of Ukrainian President Petro Poroshenko during a presidential election campaign rally of the incumbent president in Kiev on March 17. 2019. - Ukraine's Presidential elections will be held on March 31, 2019. (Photo by Genya SAVILOV / AFP)

Activists and supporters of the Ukrainian far-right party National Corps take part in a rally on the Independence Square in Kiev on March 16, 2019, to demand hard punishment for Oleg Gladkovsky and his son, businessman Igor. - Oleg Gladkovsky, a former deputy head of the national security council, profited from the sale of smuggled Russian military parts to state defence companies at inflated prices, according to a report this month by an independent media outlet. Accusations of self-enrichment at the expense of the army are particularly damaging in Ukraine, which has been fighting Russian-backed separatists in the east since 2014. (Photo by Sergei SUPINSKY / AFP)