The shelling of the Zaporizhzhia nuclear power plant in Ukraine has drawn condemnation and concern.

Ukrainian President Volodymyr Zelenskyy condemned Russia for Friday's attack on the plant, which has been seized by Russian troops, calling it "an open, brazen crime" and "an act of terror."

Russia's defense ministry blamed the shelling on the Ukrainian side.

The International Atomic Energy Agency said on Saturday it had been informed by Ukraine that "the shelling had damaged the plant's external power supply system." The agency also said the attack "triggered the emergency protection system of one of the plant's three operating reactors." Ukraine also reportedly told the agency that this unit was disconnected from the grid.

The IAEA quoted Ukraine as saying that "there had been no damage to the reactors themselves, no radiological release and no reports of injuries."

IAEA Director General Rafael Mariano Grossi said in a statement that military action jeopardizing the safety and security of the plant is "completely unacceptable and must be avoided at all costs."

The Institute for the Study of War said on Saturday that Russian forces are likely using the plant "to play on Western fears of a nuclear disaster in Ukraine in an effort to degrade Western will to provide military support."

The US think tank also said Russia is "also effectively using the plant as a nuclear shield to prevent Ukrainian strikes on Russian forces and equipment."

Fighting in eastern Ukraine has become deadlocked. Russian forces are believed to be facing fierce counterattacks from Ukrainian troops in the south.

The British defense ministry said on Sunday it is highly likely that the poor performance of Russian forces had resulted in "the dismissal of at least six Russian commanders since the start of hostilities."

The ministry also said "these dismissals are compounded by at least 10 Russian Generals killed on the battlefield in Ukraine. The cumulative effect on consistency of command is likely contributing to Russian tactical and operational difficulties."