Turkey on Wednesday condemned as not legitimate the U.S. move to exclude it from the F-35 stealth fighter jet program over Ankara’s purchase of a Russian missile defense system and called on Washington to reverse the decision.

“This one-sided step neither complies with the spirit of alliance nor is it based on legitimate reasons,” Turkey’s Foreign Ministry said in a statement, according to Agence France-Presse. “It is unfair to remove Turkey, one of the partners in the F-35 program,” the ministry added, dismissing claims that the Russian S-400 system would pose a danger to the F-35.

Turkey has ordered more than 100 of the F-35 jets, spending $1.4 billion while its defense industry has invested significant sums into production. “We invite the U.S. to take back this error which will pave the way to irreparable damage to our strategic relations,” the ministry added.

Earlier on Wednesday, the United States confirmed Turkey’s expulsion from the program after repeated warnings.

The US-made F-35 Joint Strike Fighter “cannot coexist with a Russian intelligence-collection platform that will be used to learn about its advanced capabilities,” White House spokeswoman Stephanie Grisham said.

Under Secretary of Defense for Acquisition and Sustainment Ellen M. Lord said the F-35 relies on its advanced stealth abilities and cannot co-exist with a Russian intelligence-collection platform, and as such, Turkey’s continued involvement with the F-35 program has been rendered impossible.

Following months of extended tensions over the purchase, delivery for the S-400 systems started on July 12 to an airbase near Turkey’s capital Ankara. On Sunday, Turkish President Recep Tayyip Erdoğan said the deal was the most significant contract in modern Turkish history.