Turkish President Recep Tayyip Erdogan has reaffirmed his country's purchase of a Russian-made missile defense system.

In spite of repeated warnings from the United States, Erdogan said Friday that deliveries of the S-400 system will begin in July.

On Wednesday, U.S. Vice President Mike Pence said Turkey was risking its NATO membership and its participation in the F-35 Joint Strike Fighter program.

The Turkish president said they had offered to also buy the U.S.-made Patriot system but that the U.S. offer was not as favorable as Russia's.

The U.S. and other NATO allies have said the S-400s cannot be operable alongside other allied systems and that their use in Turkey could jeapordize F-35s security.

Erdogan also said deliveries of F-35s were continuing and Turkish pilots were being trained.