DHS issued a notice to law enforcement agencies at the federal, state and local level that al Qaeda discussed plans to derail trains by placing obstructions on tracks over bridges and valleys.
The plan was supposed to be carried out on the 10th anniversary of the Sept. 11, 2001 attacks, but no specific city or rail system was identified in the notice, according to CNN. A public statement from DHS only referred to 'potential plots directed at the U.S. rail sector.'
The Transportation Security Administration, part of DHS, also sent an advisory to railroads and other entities that manage or oversee the industry.
DHS has not raised its alert level because officials say there is no credible danger at this time.
Sen. Susan Collins, chairman of the Homeland Security and Governmental Affairs Committee, has urged DHS to raise the threat level for two weeks as a precaution while the data seized from bin Laden's hideout is analyzed.
'We have no information of any imminent terrorist threat to the U.S. rail sector, but wanted to make our partners aware of the alleged plotting; it's is unclear if any further planning has been conducted since February of last year,' DHS spokesman Matt Chandler said in a statement.
In the wake of Sunday's killing, DHS is reviewing protective measures for critical infrastructure, transportation systems and other potential targets, deploying additional officers to non-secured areas at airports and identifying new targeting rules to strengthen risk assessments for passengers and cargo headed to the United States, he said.
Al Qaeda groups have attacked rail systems in Spain and elsewhere in the past.
Attacks on New York, Washington, Los Angeles and Chicago on major holidays or other significant dates were also being considered by al Qaeda, reports said. Officials again noted the documents revealed the terror group's aspirations and not any operational planning to achieve those goals.
