SBU chief in the Lviv region Viktor Andriichuk said, Censor.NET reports citing Interfax-Ukraine.
"The four detainees have been indicted for preparation of a terrorist attack. The places of six people involved in the case have been searched," he said at a briefing in Lviv on Tuesday.
According to Andriichuk, weapons and ammunition seized from the detainees will be given to the Ukrainian military in the anti-terrorist operation area.
Commenting on the statement by the Organization of Ukrainian Nationalists leader on the detention of three OUN members, Andriichuk said that "the SBU is an apolitical institution that abides by the secrecy of investigation and does not disclose data on the party affiliation of detainees."
He also said that one of the detainees had a training manual describing in detail the mechanism of setting up a cell of organization aimed at toppling government, including by force of arms.
"This case involves a lot of interesting things, but I still can not announce any of them over the secrecy of investigation," Andriichuk remarked.