Tehran, Iran – Three weeks after Iran and the United States signed a memorandum of understanding to extend their ceasefire, their truce remains fragile.Three tankers have been hit in the Strait of Hormuz over the past two days, even as Iran and the US are expected to restart mediated negotiations to end the war next week, after the funeral of Iran’s Supreme Leader Ayatollah Ali Khamenei.The US military on Wednesday launched large air attacks on …