Osaka, Japan (CNN) President Donald Trump is set to come face-to-face with Turkish President Recep Tayyip Erdoğan Saturday in Osaka, Japan, amid a dispute between the two countries over Turkey's purchase of the Russian S-400 missile system and sharp divide over who is responsible for the death of journalist Jamal Khashoggi.

In April, Vice President Mike Pence warned Turkey against moving forward with the purchase of the Russian air defense system.

"We'll not stand idly by while NATO allies purchase weapons from our adversaries, weapons that threaten the very cohesion of this alliance," Pence said.

US officials have warned Turkey that it would not be allowed to buy the F-35 stealth jet if it goes ahead with the missile system purchase because the US believes the Russian system is incompatible with the F-35 jet -- and has argued that Moscow could use it to gather intelligence on the aircraft.

Congress has threatened to impose sanctions in response, but Erdoğan said recently he doesn't believe Trump will move forward with the sanctions because of their warm relationship.