Iran's Supreme Leader says US breaches show Trump's signature is 'worthless'

July 18 (Reuters) - Iran's Supreme Leader Mojtaba Khamenei said in a written statement on Saturday that repeated U.S. breaches of a memorandum of understanding signed by the presidents of Iran and the United States had shown that President Donald Trump's signature was "utterly worthless and devoid of credibility." Washington and Tehran have exchanged strikes after a ceasefire agreement fell apart last week, raising fears of a return to all-out war.