Singapore, April 13 -- Two empty supertankers attempted to make their way through the Strait of Hormuz and into the Persian Gulf on Sunday, only to make a last-minute U-turn just as peace negotiations between the US and Iran broke down, threatening a fragile ceasefire. A trio of very large crude carriers - all without direct links to Iran - began to approach the narrow waterway from the Gulf of Oman late on Saturday, ship-tracking data show, arriving near Iran's Larak island early on Sunday. At that effective checkpoint, Iraq-bound Agios Fanourios I and Pakistan-flagged Shalamar, destined for Das island in the United Arab Emirates, turned back. A third VLCC, Mombasa B, was sailing ahead and made its way between Larak and Qeshm islands, an I...