US warns of transport bomb attack

By Justin Webb
BBC Washington correspondent

Railways could be among the targets, the department warned

The US Department of Homeland Security has warned that bombs hidden in luggage could be used to attack buses and railways in big US cities this summer.

The warning came in a bulletin issued to police, local governments and the transport industry.

The department said it was made in the light of the recent attacks in Madrid.

There is said to be a specific threat, though it comes from an uncorroborated source described by one official as "only somewhat credible".

According to the bulletin issued to local authorities, the plot - if it exists - calls for the use of improvised explosive devices.

The devices could possibly be constructed of fertiliser and diesel fuel and concealed in luggage and carry-on bags, including duffle bags and backpacks.

The bulletin also warns transport managers to safeguard uniforms, badges, ID cards and other forms of official identification.

It says terrorists may exploit such items to gain easier access to areas not normally accessible to the general public.