Russian troops seized control of Europe’s largest nuclear power plant in southeastern Ukraine before dawn on Friday, according to Ukrainian officials, but a fire set off by a raging gun battle had been extinguished.

The fighting and fire had raised worldwide alarm because of the potential that they could reach and damage the nuclear reactors and cause a radiation leak.

International monitors said early Friday that there was no immediate sign that radiation had leaked from the Zaporizhzhia plant. A Ukrainian agency said the fire had been contained to a training facility on the perimeter of the complex.

There was damage to “the structure of the reactor compartment” at one of the six reactors, which the state inspectorate said did “not affect the safety of the power unit”. That information came after the fire was put out but before it was clear that the Russians were in control of the facility.

However, there were many remaining dangers - from workers being unable to do their critical jobs while the plant is occupied to the possibility of unreported damage at one of the reactors.

The site has many acres of open pools of water where spent fuel rods have been cooled for years. Errant shells or missiles could set off radiological disasters.

The Russian defence ministry said its forces had taken control of the facility to foil a “monstrous provocation” by the Ukrainian government.

Elsewhere in Ukraine, Russian forces besieged and bombarded several cities. The southeastern port city of Mariupol has been encircled and shelled. However, Nato allies on Friday rejected Ukraine’s appeal for no-fly zones, saying that stepping in directly would lead to a broader, even more brutal European war.