Moscow  -  Moscow on Saturday mounted a “counter-terror operation” in three border regions adjoining Ukraine to halt Kyiv’s advance deeper into Russia and warned that the fighting endangered a nuclear power plant. Ukrainian units stormed into Russia’s western Kursk region on Tuesday morning in a shock attack, the largest and most successful cross-border offensive by Kyiv of the two-and-a-half year conflict.

Its troops have advanced several kilometres and Russia’s army has rushed in reserves and extra equipment, including convoys of tanks, rocket launchers and aviation units -- though neither side has given precise details on the extent of the forces they have committed. Russia’s nuclear agency on Saturday warned the Ukrainian attack posed a “direct threat” to the nearby Kursk nuclear power station.

At least 16,000 civilians have left their homes in Russian border areas, where emergency aid and medical supplies have been ferried in, and extra trains to the capital Moscow have been put on for people fleeing.

“The war has come to us,” one woman from the border zone told AFP at a Moscow train station on Friday, declining to give her name.

Russia’s army, which confirmed Saturday it was still fighting off the Ukrainian incursion, said Kyiv initially despatched around 1,000 troops, and more than two dozen armoured combat vehicles and tanks. Though on Saturday it since claimed to have destroyed around five times as many pieces of military hardware. AFP could not verify those numbers and both sides have repeatedly been accused of inflating the number of enemy losses while downplaying their own setbacks.