The two countries are holding a joint military drill
Russian S-400 missile systems
The deal has led to a strong dispute between the US and Turkey
The most severe package would all but cripple the already troubled Turkish economy
Washington and Ankara are at loggerheads over the deal of Turkey with Russia
Russia said it would deliver the S-400 missiles in July
The acting US Defence Secretary said he had talked with his Turkish counterpart
The U.S. ambassador to NATO spoke to CNBC
The Level 3 advisory tells citizens to stay with westerners and stay away from crowds
The relations between Turkey and the US have been on the low
The new system replaced the old S-300 missiles