Colombia 'dirty bomb' plot seen as unlikely

Even as they downplayed the threat from about 66 pounds of degraded or depleted uranium Colombian officials said they found and had linked to FARC guerrillas, the U.S. officials said they were not dismissing Bogota's claim that the rebel group intended to procure deadly weapons.

"I think you have to take at face value what the Colombians are saying," said a senior U.S. intelligence official, who, like others, spoke on condition of anonymity when discussing intelligence assessments. "There's no reason at this point to think they're making this up."

But the officials said the material appeared to be an easily obtained kind of uranium that poses little, if any, health hazard.

State Department spokeswoman Heidi Bronke said U.S. officials had so far heard only initial reports of the seizure from Colombian officials, and understood from them that it was depleted uranium.

She said that U.S. officials didn't know how the rebel group, the Revolutionary Armed Forces of Colombia, intended to use the material, but hoped that Colombian authorities would be able to determine that through their investigation of laptop computers and other evidence seized in a March raid that killed a top FARC commander.

Depleted uranium is not sufficiently radioactive to be suitable for a device that could be used as a dirty bomb, said Charles Ferguson, a nuclear affairs specialist at the Council on Foreign Relations.

Such devices are intended to spread highly radioactive material over a large area to cause contamination and panic.

A bomb made with depleted uranium might "have panicked people for a little while, but the alarm wouldn't have lasted" once the public realized that the health threat was negligible, he said.

Colombian forces crossed into Ecuador in the March 1 raid, killing FARC second in command Raul Reyes and seizing laptop computers and other evidence. According to the Colombian government, the laptops contained e-mail and other indications of efforts by the FARC to buy and sell uranium, as well as shoulder-fired missiles from Libya, and to blow up pipelines and commit other illegal acts.