NATO Secretary General Jens Stoltenberg has called on the alliance's members to ease the prohibition on using weapons they supply to Ukraine to strike military targets in Russia.

Stoltenberg made the remark in an interview with Britain's Economist magazine on Friday. It came as Russia intensifies its offensive in the eastern Ukrainian region of Kharkiv.

There are growing calls to lift the restrictions that limit Ukraine's use of Western-supplied weapons to within its territory.

But the administration of US President Joe Biden is cautious about taking such a step. The United States is the largest arms provider to Ukraine.

Stoltenberg said that to deny Ukraine the possibility of using Western-provided weapons "against legitimate military targets on Russian territory makes it very hard" for Ukrainians to defend themselves.

The NATO chief also said, Ukraine has the right to defend themselves, and that includes striking targets on Russian territory.

He did not mention the US by name. But he made it clear that Washington and other NATO members should ease their restrictions.