Ukraine has deployed thousands of troops in a major incursion into Russia’s western Kursk region, in a bid to “stretch” and “destabilise” Russia, a senior Ukrainian security official told AFP.

Ukrainian units stormed into Russian territory on Tuesday in a surprise attack that has developed into the most significant cross-border assault by Kyiv since the conflict began in February 2022.

“We are on the offensive. The aim is to stretch the positions of the enemy, to inflict maximum losses and to destabilise the situation in Russia as they are unable to protect their own border,” the official said late Saturday, speaking on condition of anonymity.

The Russian army earlier said Ukraine had deployed around 1,000 soldiers in the incursion which appeared to catch the Kremlin off guard with Ukrainian forces successfully penetrating Russian defensive lines.

Asked whether 1,000 Ukrainian troops were taking part in the assault, the official said: “It is a lot more… thousands”.

The offensive was also having an important psychological effect at home, he said.

The attack has “greatly raised our morale, the morale of the Ukrainian army, state and society”, the Ukrainian official said, speaking after weeks of Russian advances in eastern Ukraine.

“This operation has shown that we can go on the offensive, move forward,” the official said.

“It seems that the Russians have problems with coordination, preparedness for action,” he said.

But he said there had been little effect so far on fighting in the east.

“The situation is basically unchanged. Their pressure in the east continues, they are not pulling back troops from the area,” he said, adding only that “the intensity of Russian attacks has gone down a little bit”.