By Menna AlaaElDin and Kanishka SinghCAIRO/WASHINGTON, Aug 22 (Reuters) - The United States and Iran exchanged defiant messages ahead of Monday's scheduled announcement of new U.S. economic sanctions that could impact the Islamic Republic and Tehran's most important trading partners including China.

U.S. sanctions on Iran are tightening, targeting its oil trade and global financial networks as Washington seeks to force Tehran to change course

Trump threatens new Iran economic crackdown as US-Iran conflict escalates, with rising tensions over the Strait of Hormuz and regional diplomacy