SBU Chief Vasyl Hrytsak said this at a briefing on Wednesday, an Ukrinform correspondent reports.
"On October 9, 2017, the SBU's main office in Donetsk and Luhansk regions detained two Ukrainian citizens, who, on the order of the 'MSS of the DPR,' were plotting a terrorist attack in Mariupol," Hrytsak said.
He added that SBU officers had managed to prevent a series of attacks, the first of which was to take place directly at the railway station in Mariupol.
"The terrorist attack was planned in relation to the passengers of a Mariupol-Kyiv train. The exact date had to be determined by those who organized this terrorist attack," Hrytsak said.
According to counterintelligence, the target of the attackers was not military facilities, but crowded places.
According to Hrytsak, saboteurs received tasks from representatives of the so-called "Ministry of State Security of the Donetsk People's Republic." The organizer of a sabotage group is "DPR" militant Dmytro Zabutsky, who has been became known since 2014.
"It was Dmytro Zabutsky who was tasked with picking up a sabotage group from among his friends who live in the territory under the control of the Ukrainian authorities. According to the plans of the Russian special services, terrorist attacks should have led to destabilization of the situation in Mariupol itself and in the ATO zone, throughout Ukraine, so as to show the failure of Ukrainian law enforcement agencies and the Ukrainian state to ensure the safety of civilians," Hrytsak said.