A Russian state-owned news agency says its office in the Ukrainian capital has been raided and that at least one of its correspondents has been detained for questioning.

RIA Novosti said on Tuesday that Ukrainian intelligence officers stormed its office in Kiev and that it has been unable to get in touch with its correspondents there since.

Ukrainian security agency SBU said in a statement that it is investigating "a network of media outlets" controlled by the Russian government which are "used as tools in a hybrid war against Ukraine."

Relations between Moscow and Kiev soured in 2014 when Russia annexed Ukraine's Crimea and threw its weight behind separatists in eastern Ukraine. More than 10,000 people have died in the long-simmering conflict in the industrial east.