One of Russia's top spymasters said on Monday he hoped that the U.N. nuclear watchdog and the European Union would look into Ukrainian nuclear activity that he said might signal Kyiv was working on a "dirty bomb".

Sergei Naryshkin, the head of Russia's SVR foreign intelligence service, did not provide documentary evidence to back his assertions.

The Ukrainian defence ministry did not immediately respond to a request for comment. Kyiv has in the past said it takes its responsibilities for nuclear power very seriously while accusing Russia of recklessness when it comes to its control of the Zaporizhzhia nuclear plant in southern Ukraine.

Naryshkin said in a statement that his service had information that a batch of "irradiated fuel" had secretly been sent from the Rivne nuclear plant in western Ukraine for disposal at a spent fuel storage facility in Chornobyl.

He said the action, which Reuters could not independently verify, was suspicious and could only be explained by Kyiv intending to create a "dirty bomb", combining radioactive material with conventional explosives.

Russia has previously accused Ukraine, without providing evidence, of planning to use such a "dirty bomb", amid fears on both sides that fighting around the Zaporizhzhia nuclear plant, which Russian forces seized a few days after invading Ukraine early last year in what Moscow calls its "special military operation", could lead to a disaster.

(Reporting by Reuters; Editing by Andrew Osborn and Kevin Liffey)