WASHINGTON - Every one of the more than 825 F-35 fighter jets delivered so far contain a component made with a Chinese alloy that's prohibited by both US law and Pentagon regulations, according to the programme office that oversees the aircraft.

The component - a magnet used in an aircraft-powering device supplied by Honeywell International - has been used in the plane since 2003, the Pentagon's F-35 programme office said.

On Wednesday, the Pentagon suspended deliveries of new F-35s to make sure the programme complies with regulations related to "specialty metals."

The F-35 programme - which may result in over 3,300 jets - will now seek a national security waiver from the Pentagon's top acquisition official to resume deliveries of already assembled new aircraft containing the alloy, F-35 spokesman Russell Goemaere said.

The programme office does not anticipate "replacing magnets in delivered aircraft," he said.

Replacing them could entail costly and time-consuming retrofits of the over 500 US training and operational aircraft.

The Pentagon and Lockheed Martin, which builds the aircraft, have found a US source for the alloy for future planes, the company said.

"Further investigation is under way to understand the causal factors for the non-compliance and to establish corrective action," Goemaere said.

US law and Pentagon acquisition regulations prohibit the use of specialty metals or alloys made China, Iran, North Korea or Russia. The Defence Contract Management Agency reported the violation to the F-35 programme office on Aug 19.

A decade ago, the Pentagon granted a waiver to Honeywell to use Chinese magnets in other F-35 components, saying the programme, already beset by delays and cost overruns, would have been slowed even more.

The part has no technical flaw and it poses no security risk to the US's top stealth fighter or its eight million lines of software code.

Rather, it's a question of supply-chain security and why the banned alloy was not detected by Honeywell.

The Pentagon's judgment that China poses the biggest threat to the US globally only adds to the challenge.

When the halt was announced, Honeywell said it was working with the Pentagon and Lockheed, and was "committed to supplying high-quality products that meet or exceed all customer contract requirements."

Spokesman Adam Kress said the company has no additional comment.

The device in question is a magnet contained in a Honeywell turbomachine that integrates the aircraft's auxiliary power unit and an air cycle machine into a single piece of equipment that provides electrical power for ground maintenance, main engine startup and emergency power.

It includes a cobalt and samarium alloy "recently determined to be produced in the People's Republic of China" and magnetised in the US, the F-35 programme office said.

It was provided to a Honeywell subcontractor by a lower-tier supplier, Lockheed Martin said.

"We are working with our partners and DoD to ensure contractual compliance within the supply chain," Lockheed Martin spokeswoman Laura Siebert said in statement.

"We are working with the DOD to resolve the issue as quickly as possible to resume deliveries."

Lockheed Martin delivered 88 of a contracted 148 F-35 jets this year before the halt. BLOOMBERG