Turkish President Recep Tayyip Erdogan announced the signing of the S-400 air defence system with Russia at his party's group meeting. Erdogan responded to criticism that the S-400 system would cause a tension within NATO, saying, “Why does the S-400s cause tension? A country has to make the most ideal search for its own security. We have been searching for such things for years, if we can not do what we want with the US. Greece has been using the S-300 system, which is a NATO country for years… Why are they disturbed? We have now taken steps to deal with this issue with the Russian Federation, signatures have been issued and I hope we will see the S-400 missiles in our country. And we will proceed with joint production.” US Chief of Staff Joseph Dunford recently said, “Turkey has not purchased S-400 air defence systems from Russia. If they had done this, it would have been worrying, but they did not.”