Suspected missile warhead parts in transit to Iran have been seized by UK Border Force inspectors at London’s Heathrow Airport.

The find came during an inspection of freight departing the airport. At least two “O rings” — which can be used to form seals in rockets — were detected, the Evening Standard reports.

The suspect items were marked for use in the Iranian oil industry, however Border Force staff halted the shipment after becoming suspicious that the real intention was to use them in missile construction.

Monique Wrench, the UK Border Force’s deputy director at Heathrow, told the Standard the suspected illicit items had been confiscated as part of staff “counter-proliferation” work.

“We had a couple of O rings that we identified. O rings are pieces of rubber that go between tubes to stop leakage to seal them. They can be used in oil, but they can also be used for warheads and the like. Our staff stopped them from going to Iran.

“It is a component part. It looked like it was going to an oil refinery. But the dots don’t quite join up here.”

The “sale, supply, transfer or export of missile-related goods and technology” to Iran is banned under sanctions enforced by Britain and other countries.

Last December, the U.S. displayed incontrovertible proof Iran has violated multiple U.N. Security Council resolutions against weapons proliferation in the form of missile parts and explosives recovered from Middle Eastern battlefields by America’s allies.

U.N. Ambassador Nikki Haley said the find reinforced a United Nations report that portrays Iran as a regional “arsonist” that is sworn to the destruction of Israel.