A spokesperson for the SBU Security Service of Ukraine says a statement by Russia's FSB Federal Security Service on links between the Ukrainian intelligence services and Islamic State (ISIS) is a complete fabrication.
"We will not comment on the fabrication," Press Secretary of the Ukrainian SBU Security Service's chief Olena Gitlianska told the BBC News Ukraine outlet.
The FSB earlier reported it had allegedly detained an ISIS member who masterminded the assassination of a leader of the so-called "Donetsk People's Republic" ("DPR"), which is controlled by Russia.
The man allegedly confessed that the "Ukrainian special services are actively assisting ISIS fighters, providing money, weapons and explosives for terrorist attacks in Russia."
The SBU said the report was fake.
According to the Russian side's story, a resident of Dagestan, Medzhid Magomedov, acted "on the instructions of the SBU and the Right Sector."
The FSB alleges that early this year Magomedov arrived in Ukraine where he contacted the SBU.
"Magomedov was instructed by officers of the Ukrainian special services to eliminate a 'DPR' commander residing in Smolensk region," the Russians said.
During Magomedov's arrest, the FSB officers found a homemade explosive device, a gun and ammunition.
As UNIAN reported earlier, "DPR" leader Alexander Zakharchenko was killed in an explosion in a Donetsk restaurant on August 31.
Russian-controlled militants in the temporarily occupied territory of Donetsk region claimed a "Ukrainian trace" in the blast, while Russia's Ministry of Foreign Affairs echoed the accusations.
The Ukrainian SBU, for its part, did not rule out the Russian special services' involvement in the assassination, adding that local feuds between local terrorist leaders could be the cause.