On Thursday, Ukraine accused Russia of shooting on a pre-approved route for an investigation team en route to the country's Zaporizhia nuclear power facility to guarantee its safety.
Energoatom, the country's official nuclear organisation, claimed that a Russian fire had triggered the plant's security systems, causing it to shut down one of its generating units.
Russian officials in turn accused Ukraine of being responsible for the outbreak of fierce fighting around Europe's largest plant.
The Russian Defense Ministry said Thursday that a Ukrainian "sabotage group" consisting of about 60 people landed ashore within two miles of the plant.
The ministry also accused Kiev of firing at the meeting place of the IAEA mission with Russian experts in the area of settlement of Vasilivka and the plant.
The U.N.'s Atomic Energy Agency has warned for months about the risk of a nuclear disaster and has sought to send a team to inspect and help secure the plant.