Travelers to the United States will henceforth be screened if they are carrying radioactive material.

According to The New York Times this measure is meant to prevent terrorists from ferrying any radioactive substances into the US.

There have been fears in recent months that the next terrorist attack on the US may involve a nuclear device.

Last week, Mansoor Ejaz, who has been involved in Track II diplomacy in South Asia, speculated in an op-ed column in The Weekly Standard magazine that Osama bin Laden may personally carry out a suicide attack utilising atomic weapons targeting the West Coast of the United States.

Scores of customs agents armed with advanced portable radiation detectors patrolled Times Square, the traditional venue of New Year Eve celebrations in the US on January 31, 2001, for fear that the dense crowds there may be targeted by nuclear-armed terrorists.

Random checks for radioactive material are already enforced at many entry points in the United States, most notably at its border with Canada. The checks pre-date 9/11 and first became apparent just before New Year 2000 when US intelligence were alerted about the possibility of a Millennium Eve nuclear-related terror attack.

Beginning March 1, these checks will be enforced throughout the US. About 500,000 visitors will be screened every day for radioactive material. About 7,000 portable radiation detectors have been employed for the operation.

Importantly, all trucks entering the US will be checked for atomic material. But air and sea-borne cargo -- the likeliest avenues of radioactive transportation -- will only be examined randomly. The newly formed US Department of Homeland Security Department hopes to enforce checks of all such cargo before the year-end.

For months now, US intelligence have worried about the likelihood of a 'dirty bomb' -- radioactive material dispersed by a conventional bomb -- being detonated by terrorists in the country. Rohan Gunaratna, the Sri Lankan-born expert on Al Qaeda, warned in an interview to India Abroad, the newspaper owned by rediff.com last year, that bin Laden had obtained the necessary know how to detonate a dirty bomb, possibly from renegade Pakistani nuclear scientists sympathetic to his cause. This information has been confirmed by Al Qaeda operatives now in US custody.