Russia, Turkey to develop military ties despite US sanctions
US Secretary of State Mike Pompeo at the time told Turkish Foreign Minister Mevlut Cavusoglu that the American sanctions were intended to prevent Russia from receiving substantial revenues from the sale.
He added that Russian President Vladimir Putin appreciated Turkey's determination to "continue cooperation in this area despite continuing illegitimate pressure from Washington."
"We prefer to solve all issues including that of the S-400 through negotiations," Cavusoglu said in comments translated into Russian.
"After introducing the sanctions the US announced it favours dialogue. We've never been against dialogue," the Turkish foreign minister added.
The two countries are jointly monitoring a Russian-mediated truce over the disputed Nagorno-Karabakh region after a six-week war between Armenia and Azerbaijan that claimed more than 6,000 lives.
Tensions between the two nations had risen over Nagorno-Karabakh while the fighting was ongoing, with Russia accusing Turkey of deploying Syrian fighters to combat Armenian forces in the contested region.
Earlier this month Turkish police briefly arrested two Russian journalists in Istanbul for allegedly filming a drone production unit without permission.