Some of the first information gleaned from Osama bin Laden's compound indicates al-Qaida considered attacking US trains on the upcoming anniversary of the September 11 attacks.
But counter-terrorism officials say they believe the planning never got beyond the initial phase and have no recent intelligence pointing to an active plot for such an attack.
As of February 2010, the terror organisation was considering plans to attack the US on the 10th anniversary of the 9/11 attacks.
One idea outlined in hand-written notes was to tamper with an unspecified US rail track so that a train would derail at a valley or a bridge, according to a joint FBI and Homeland Security bulletin sent to law enforcement officials around the country.
The al-Qaida planners noted that if they attacked a train by tilting it, the plan would only succeed once because the tilting would be spotted the next time.
Information on the train plot appears to be the first widely circulated intelligence pulled from the raid this week on bin Laden's secret compound in Pakistan.
After killing the terror leader and four of his associates, US Navy Seals confiscated a treasure trove of computers, DVDs and documents from the home where officials believe the al-Qaida chief had been hiding for up to six years.
Other intelligence information gathered at the compound represented a terrorist wish list but has revealed no specific plan so far, a US official said.
He added that documents indicated a desire to hit the US with large-scale attacks in major cities and on key dates such as anniversaries and holidays. But there was no sign those plans were anything more than ambitions.
Intelligence analysts have been reviewing and translating the material seized at bin Laden's hideout, looking for information about pending plots and other terror connections.
Even before the raid, intelligence officials had been warning for years that al Qaida was interested in attacking major US cities on key dates that are uniquely American.
"While it is clear that there was some level of planning for this type of operation in February 2010, we have no recent information to indicate an active ongoing plot to target transportation and no information on possible locations or specific targets," the FBI/Homeland Security warning said.
The statement also urged local officials to be on the lookout for clips or spikes missing from train tracks, packages left on or near the tracks and other indications that a train could be vulnerable.
An official with the Association of American Railroads said the organisation has received warnings from the federal government and is sharing the information throughout the railroad network.
"We are always making sure that the system is run as safely and securely as possible," spokeswoman Patricia Reilly said.
On Monday, the FBI and Homeland Security warned law enforcement officials across the US that bin Laden's death could inspire retaliatory attacks, and terrorists not yet known to the intelligence community could be operating inside the country.