The European Union is demanding that Iran share with the U.N. atomic agency full details of its manufacture of parts for machines that could be used to make the core of nuclear arms, in a statement reflecting its concern over the sensitive issue.

The draft statement was seen by The Associated Press Friday, ahead of its planned delivery next week at a board meeting of the U.N.’s International Atomic Energy Agency and a week after the agency reported that Iran started making rotor tubes for centrifuges in June.

It demands the “full cooperation of Iran” on the issue in talks with the IAEA and calls for updates from the agency to the 35-nation IAEA board.

Centrifuges are machines that spin uranium into concentrations ranging from low-range reactor fuel to weapons-grade material for the fissile core of a warhead. Iran has 5,060 low-tech centrifuges now producing limited amounts of fuel-grade uranium, and under a nuclear deal reached last year and implemented in January it must use spare parts stripped from old or idle machines to keep them going.

Parts for more advanced centrifuges would fall under even tighter regulations. The agency needs to keep a close eye on how many rotor tubes are being made and for what models of centrifuges, to make sure they are being produced only in quantities and for machines allowed under the 2015 agreement.

Any overproduction could hint at possible plans by Iran to expand advanced centrifuge testing beyond pact limits. That could be a significant issue, considering enriched uranium is a potential pathway to nuclear arms and more technically sophisticated models can enrich uranium much more quickly than Iran’s present mainstay centrifuges.

With Iran generally in line with its obligations under the deal, past EU statements since its implementation have been generally low-key.

(AP)