Earlier in the day, Turkish Foreign Minister Mevlut Cavusoglu said that Ankara and Washington had created such a group.
"We have not yet created a working group on the S-400 issue, the technical talks are underway. The minister meant that a technical-level working group on the issue of sanctions would be set up by Turkey and the US," the source said.
In July 2019, the United States suspended Turkey's participation in its F-35 multirole fighter program over Ankara's purchase of Russian S-400 air defence systems and later completely removed it from the project. In December, Washington imposed sanctions on Turkey's weapons procurement sector over the S-400 issue. Despite that, however, Turkey continues to manufacture F-35 parts.