WASHINGTON (AFP) The United States is preparing to beef up law enforcement presence on trains and transit systems, ABC News said Monday, amid US travel alerts for a possible terrorist attack in Europe. Coinciding with counterparts in Europe, US train network Amtrak will hold a Rail Action Day on Friday where uniformed officers will have highly visible presence on train routes. A US official told ABC News however that the exercise was long-planned and not connected in any way to the alert for Europe. The formal US travel alert warned Americans about possible terrorist attacks in Europe as American and European authorities were searching for suspects, with European railways, subways and tourist spots possibly under threat. European security officials last week said a plot or plots were uncovered suggesting Al-Qaeda militants were planning to stage simultaneous strikes in Britain, France and Germany, with a possible Mumbai-style attack in the works. The US travel alert, which was promptly backed up by British and French officials, was unusual and suggested concrete intelligence had emerged, according to a former CIA officer.