Beijing, April 13 -- Two empty crude tankers attempted to make their way through the Strait of Hormuz and into the Persian Gulf on Sunday, only to make last-minute U-turns just as peace negotiations between the US and Iran broke down, threatening a fragile ceasefire. Two very large crude carriers and one Aframax-class vessel - 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 turned back. The first VLCC, Mombasa B, was sailing ahead and made its way between Larak and Qeshm islands, an Iran-approved route into the Persian Gulf. The reasons behind the about-turns - and the third, successful passage - are not clear, as both Iraq and Pakistan had earlier received approvals from Iran to transit the strait. But the change of heart came just as negotiators in Islamabad announced they had failed to reach a deal....