Officials say President Recep Tayyip Erdogan has discussed with U.S. President Donald Trump a Turkish proposal to establish a joint committee over Turkey's plans to purchase Russian S-400 missile defense systems.

A statement from Erdogan's 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.

Turkey's decision to purchase the advanced Russian system has deepened a rift between the NATO allies.

U.S. officials say the Russian defense system could pose a threat to a U.S. 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.