Trump sent second letter to Erdogan threatening sanctions over S-400s
Letter set out US conditions for resolving crisis over Russian-made missiles ahead of White House meeting, but Turkish president was not convinced, sources say
Diplomatic Thriller: Jihadist trapped in Greece-Turkey dead zone (photo)
He is an American national who had joined ISIS
US: Warning message to Turkey over Greek continental shelf
The US publicly condemned the Turkish drillings as provocative and undermining the confidence it should have in the Cyprus negotiations