ANKARA, Turkey (AP) — Turkish President Recep Tayyip Erdogan says a U.S. F-35 fighter aircraft program that excludes Turkey would be “doomed to a total collapse.”

Erdogan made the comments Tuesday at a defense industry fair amid warnings from Washington that Turkey’s decision to purchase the Russian S-400 missile system will jeopardize Turkey’s participation in the F-35 program.

The issue has deepened a rift between the NATO allies. Washington says the S-400 would pose a threat to the F-35 program; Turkey rejects the claim and wants a joint committee to review the possible risks.

Erdogan said: “Turkey does not accept any impositions in the defense field, nor will it” in the future.

He said Turkey has taken steps to produce its own fighter plane and is also planning to build unmanned fighter planes.