The U.S. military is due to begin a blockade of ships entering or leaving Iran's ports at 10 a.m. (1400 GMT), after weekend talks on ending the war broke down.Tehran has threatened to retaliate against ports of its Gulf neighbors.The ceasefire, which halted six weeks of U.S. and Israeli airstrikes, is under threat, with only a week left to run.Oil prices surged when trade reopened on Monday, with no sign of a swift reopening of the Strait of Hor...