The issue of how to deal with Russia, which annexed Crimea in 2014 and backs pro-Russian separatists in eastern Ukraine, is prominent ahead of the vote, with incumbent Petro Poroshenko casting himself as the commander-in-chief Ukraine needs to defend the country.
Vasyl Hrytsak, the head of the SBU, the main intelligence agency, told a news conference in Kiev that seven members of the Russian group had been detained and charged and that an eighth person had been detained on Wednesday morning.
Two of the group's members were Russian citizens, said Anatoly Matios, Ukraine's military prosecutor, describing them as staff officers of Russia's GRU military intelligence agency. The other six were Ukrainians.
There was no immediate reaction from Russia's GRU.
The SBU has reported before that it captured groups belonging to Russian special agencies.
"Those detained were involved in the attempted murder of an employee of the Ukrainian defense ministry's intelligence service...in Kiev in April," said Matios, adding the group had planted a bomb beneath the man's car which had gone off prematurely, badly injuring one of the accused.The SBU released a video of the same incident which showed a man placing the bomb under a car before a big explosion. The video showed a man lying in a hospital bed with part of his right arm missing saying he was Russian and born in Moscow.