Russian military forces have been enhancing defensive positions in and around the Zaporizhzhia nuclear power plant in recent weeks, four witnesses told the Reuters news agency.
New trenches have been dug around the city, and more mines have been laid.
The measures described by two Ukrainians who work at the power plant and two other residents in the city of Enerhodar underline the risks the war poses to the facility’s security.
The sources spoke on condition of anonymity because of fears for their safety.
The four sources said they heard occasional blasts, which they assumed were from stray animals stepping on mines.
One of the workers also saw tracer bullets fired across from the roof of one of the plant’s buildings, most likely at a drone.