By Robert Harvey LONDON, Jan 29 (Reuters) - Brent oil futures prices jumped on Thursday, hitting a four-month high on rising concerns of a possible U.S. military attack on ​Iran, OPEC's fourth-largest producer, with output of 3.2 million barrels per day. "The immediate (market) ‌concern ... is the collateral damage done if Iran takes a swing at its neighbours or possibly even more tellingly, it ‌closes the Strait of Hormuz to the 20 million barrels per day of oil that navigates it," said PVM analyst John ...