Al Qaeda and other terrorist groups could be targeting buses around the nation because they are easier to attack than airplanes, according to the TSA.

The announcement reminds law enforcement officials that bus attacks are more common than attacks against the airline industry, with more than 725 bus attacks from 2004 through 2009.

 Information about the new threat comes from a TSA bulletin called "Terrorist Concerns Regarding Mass Transit Bus Systems."

'It's something that we've seen in reporting over time that terrorists around the world clearly are interested -- because of the accessibility, the open architecture -- both of buses and rail,' Transportation Security Administration Director John Pistole said. 

Intelligence recovered at Osama bin Laden's compound shows the Al Qaeda leader considered using buses to ram into buildings in the United States, Fox News reported.

TSA said there are no indication terrorist groups have immediate plans to attack buses.  Nonetheless, the TSA bulletin warns that terrorist groups could be trying to recruit employees or 'insiders' who work in the bus, train and airline industry.