Kyrylo Vyshynsky, a dual Ukrainian-Russian national who works for Russian state-run news agency RIA Novosti, was detained in Kiev on Tuesday where officials said he would be charged with treason for his "subversive" reporting to justify Moscow's 2014 annexation of Crimea.
Ukraine's state security service searched the Kiev offices of RIA Novosti and RT. Lutsenko added that the Ukrainian investigation into those activities "has evidence of carrying out well-paid anti-Ukrainian attacks" by RIA Novosti-Ukraine.
Russia Today TV channel's editor-in-chief Margarita Simonyan said on Twitter that its office phones in Kiev appeared to be blocked and that its Ukrainian website is down after security officers raided the building.
"The aggressor country used [these media] in the context of a hybrid information warfare against Ukraine", she said.
The raids and detention came just hours before Russian President Vladimir Putin was to open a bridge that will provide the first direct road connection to the Crimean Peninsula which Moscow annexed from Ukraine in 2014.More news: Salman Khan's Race 3: Much-awaited trailer takes the internet by storm
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Relations between Moscow and Kiev soured in 2014 when Russian Federation annexed Ukraine's Crimea and threw its weight behind separatists in jap Ukraine.
"If it is the case that the actions of Ukrainian law enforcement bodies are somehow connected with the professional work of these media organisations, that would be outrageous and scandalous", Kremlin spokesman Dmitry Peskov told journalists.
They also said Vyshynsky later collaborated with separatist groups in eastern Ukraine, where a conflict that broke out following Crimea's seizure has cost some 10,000 lives.