By Andrea ShalalWASHINGTON, Aug 22 (Reuters) – U.S. President Donald Trump has vowed to hit Iran hard economically, after Treasury Secretary Scott Bessent said that Washington would impose measures on Tehran that have "never been seen" as soon as next week.Bessent is due to hold a press conference at ?2 p.m. EDT (1800 GMT) on Monday.The United States, ?United Nations and European Union have applied sanctions, implemented trade embargoes and frozen assets since the late 1970s over Iran's nuclear program, human rights violations and support for militant groups.Since the Iran war began in February, Washington has levied additional maritime, energy…