Ukraine was fully within its rights to launch its surprise offensive into Russia's Kursk border region as an act of self-defence, NATO chief Jens Stoltenberg told German newspaper, Die Welt, Paralel.Az reports.

The offensive launched on August 6 caught the Kremlin off guard, with Kyiv claiming to have captured dozens of settlements and more than 1,200 square kilometers (nearly 500 square miles) of territory.

"Ukraine has a right to defend itself. And according to international law, this right does not stop at the border," Stoltenberg said in an interview with Die Welt published Saturday. "The Russian soldiers, tanks, and bases there (Kursk) are legitimate targets under international law."

The offensive also surprised Kyiv's allies, with Stoltenberg saying Ukraine "did not preview its planning" with NATO and that the Western military alliance "played no role".

Stoltenberg also welcomed Germany's commitment to remain Ukraine's largest European military donor and second-largest worldwide, as Berlin prepares cuts to its aid to Kyiv in next year's budget.