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Massive amounts — perhaps 100 times the amount FARC proposed selling — would be needed to extract enough of the rare isotope for one or two atomic bombs.

Moreover, the extraction process is highly technical, typically requiring thousands of connected centrifuges spinning at supersonic speeds for long periods of time.

“If it is regular uranium they are talking about, it would require a huge industrial task to convert into something that is bomb grade,” said Mr. Oelrich.

An example often cited is Iran’s attempt to enrich uranium, which would require 3,000 centrifuges continuously operating for nearly a year to produce enough material for one nuclear bomb.

Colombian officials speculated that the uranium offered by FARC could be used to make a so-called dirty bomb, in which conventional explosives are used to spread radioactive debris.

Even that would be unlikely, said Steve Kidd, of the London-based World Nuclear Association.

“In this form, [uranium] is only lightly radioactive and would be useless in a dirty bomb,” Mr. Kidd said.

The e-mail does not mention a customer by name, but it is presumed that FARC is proposing a uranium sale to Venezuela. The nation’s president, Hugo Chavez, is sympathetic to FARC and has negotiated with the guerrilla group for the release of hundreds of hostages, many of whom have been held for years.

Rep. Connie Mack, Florida Republican, on Friday proposed a resolution declaring Venezuela a state sponsor of terrorism, citing the proposed uranium sale.

Rep. Ileana Ros-Lehtinen, also a Florida Republican, backed the proposal.

“It is vital that Congress and the administration have access to the volumes of information that might determine whether [Venezuelan President Hugo] Chavez has aided the FARC in its war on the people of Colombia,” said Ms. Ros-Lehtinen.

Other documents released from the seized laptop reportedly indicate Mr. Chavez either paid or pledged $300,000 to FARC.

“It is highly conceivable that [FARC guerrillas are] trying to expand their income flows by obtaining and selling high explosives on the black market,” said John Pike of

“And it is conceivable that Venezuela”s Chavez may be intrigued by such a prospect, and certainly Iran would be,” Mr. Pike said.