Turkish President Recep Tayyip Erdogan offered US President Donald Trump the formation of a joint committee over Ankara’s plans to purchase the Russian S-400 missile defense systems, officials said. A statement from Erdogans office says the two leaders held a telephone conversation on Monday during which they also discussed the fight against terrorism and efforts to increase trade. Turkeys decision to purchase the advanced Russian system has deepened a rift between the NATO allies. US officials say the Russian defense system could pose a threat to a US F-35 fighter jet program and have warned of consequences if the purchase is finalized. Turkey denies that the system is a threat and has proposed a joint committee to review security risks.