All container cargo entering US ports will be scanned by radiation detecting equipment by the end of the year, according to Homeland Security secretary Michael Chertoff.

However, he admitted more advanced equipment is needed to help speed the process and spot a potential nuclear device or dirty bomb.

The agency also expects to scan all containers that enter through border points.

The agency has added radiation portal monitors at major seaports and facilities and now there are more than 1,000 of the devices in use.

Trucks carrying containers unloaded from ships pass through the detectors. If the machine finds signs of radiation, the container gets another scan and possibly an inspection by hand-held devices to help identify how much and what kind of radiation is present.

The ports of Los Angeles and Long Beach are among several US ports currently testing new devices, which are more efficient at distinguishing radiation from natural sources such as granite or kitty litter from the type of radiation emitted by a dirty bomb.