The US Pentagon has stopped accepting new F-35 jets after it discovered a magnet used in the stealthy fighter's engine was made with unauthorized material from China, a US official said on Wednesday, Reuters reported.

An investigation that gathered steam in mid-August found that an alloy in the engine's lubricant pump did not comply with US procurement laws that bar unauthorized Chinese content, said Pentagon spokesperson Russell Goemaere.

Goemaere confirmed the magnet does not transmit information or harm aircraft, and that there are no risks involved.

There are other Chinese-origin magnets on the jet which have received waivers from past Pentagon officials.