Russian troops left the heavily contaminated Chernobyl nuclear site early Friday after returning control to the Ukrainians, authorities said, as eastern parts of the country braced for renewed attacks and Russians blocked another aid mission to the besieged port city of Mariupol. Ukraine's state power company, Energoatom, said the pullout at Chernobyl came after soldiers received “significant doses” of radiation from digging trenches in the forest in the exclusion zone around the closed plant. But there was no independent confirmation of that. The exchange of control happened amid growing indications the Kremlin is using talk of de-escalation in Ukraine as cover to regroup, resupply its forces and redeploy them for a stepped-up offensive in the eastern part of the country. Ukrainian President Volodymyr Zelenskyy warned that Russian withdrawals from the north and center of the country were just a military tactic to build up forces for new powerful attacks in the southeast.