WASHINGTON (Reuters) - The Pentagon has suspended deliveries and activities linked to Turkey’s F-35 fighter jet operational capability, a spokesman said on Monday, unless Ankara gives up its commitment to take delivery of a Russian missile defense system.

U.S. has repeatedly warned Turkey that the Russian S-400 system it aims to buy would compromise the security of the F-35 aircraft, which is made by Lockheed Martin. Ankara, which is a production partner in the making of the stealthy jet, has so far refused to back down on its planned purchase.