International shipping vehicles vulnerable to terrorist attacks, FBI warns.(The Dallas Morning News)

LONDON _ With al-Qaida stepping up its sporadic attacks on western targets, there is a consensus among terrorism experts and the FBI that international shipping is increasingly vulnerable to suicide bombs and other extreme tactics.

The risk extends beyond the big, obvious targets _ the French oil tanker blown up off the coast of Yemen in October, for instance _ to the thousands of ferryboats that move cars, cargo and commuters from port to port, often with minimal security, in the United States and Europe.

And the threat extends inland, to the nation's railways and interstate highways, experts warn, because the container units carried into U.S. ports by ships from all over the globe are routinely transferred into rail cars or trucks without being checked for explosives or other dangerous devices.

It would be possible for terrorists to load a container with a "dirty bomb" or a chemical weapon that could be programmed to detonate at a time when the container is in the middle of a crowded urban area, warned Steven Flynn, a former U.S. Coast Guard ...