Hundreds of civilians on Sunday fled Ukrainian territories under Russian control as part of an “evacuation” ahead of what’s feared to be intense fighting around an area home to Europe’s largest nuclear power plant.

A Ukrainian mayor slammed Moscow’s move as a cover-up operation to move troops, while the U.N. nuclear watchdog raised concerns over heavy fighting during a potential spring counteroffensive when Ukrainian forces are expected to seek to regain control of territories lost to Russian control.

Russian forces announced the evacuation for 18 settlements on Friday, and over the weekend, civilians have been rushing to leave those areas. The Ukrainian mayor of Melitopol, Ivan Fedorov, called it a “mad panic” as thousands of cars were stuck on the roads with five-hour waits, BBC reported.

Meanwhile, Russian paramilitary group Wagner’s boss on Sunday signaled that his men would continue to fight in the Ukrainian city of Bakhmut, a U-turn from an earlier threat — made in a video filmed alongside dead bodies — to withdraw from there as he criticized Moscow for failing to supply his group with the ammunition it needed.

Russian defense officials reportedly had reservations about over-assisting Yevgeny Prigozhin, whose Wagner mercenaries have played a key role in securing control over Ukraine’s eastern territories.

In Bakhmut, Ukraine has accused Russia of attacking the besieged city with phosphorus munitions.

Russia’s Federal Security Services claimed on Sunday they had foiled an attempt by Ukrainian intelligence to attack a military airfield in central Russia with drones stuffed with explosives. Kyiv has not responded to the accusation but previously attributed such actions to “false flag” operations or Russians opposed to President Vladimir Putin.