In an annual report to Congress on proliferation threats, the US Central Intelligence Agency also repeated Tuesday its insistence that Iran was pursuing "a clandestine nuclear weapons program."

But it remained silent about charges made earlier this month by Secretary of State Colin Powell, who accused Iran of seeking to adapt its missiles to carry nuclear warheads.

Instead, the agency used its strongest terms to alert lawmakers to the threat of terrorist organizations using chemical, biological, radiological and nuclear materials to harm the United States and its allies, saying the danger of such an attack "remained high."

"One of our highest concerns is Al-Qaeda's stated readiness to attempt unconventional attacks against us," the report pointed out.

The CIA said analysis of an Al-Qaeda document recovered in Afghanistan in the summer of 2002 "indicates the group has crude procedures for making mustard agent, sarin, and VX."

The network that masterminded the September 11, 2001 attack, intelligence officials said, could also attempt to build a cyanide-based chemical weapon capable of producing a lethal concentration of poisonous gases in an enclosed area.

In addition, Al-Qaeda is keenly interested in radiological dispersal devices, or "dirty bombs." Construction of such a device "is well within its capabilities as radiological materials are relatively easy to acquire from industrial or medical sources," the spy agency warned.

Documents recovered by US forces in Afghanistan show that Al-Qaeda founder Osama bin Laden and his associates were engaged in what intelligence officials described as "rudimentary nuclear research."

But the CIA cautioned that the true extent of Al-Qaeda's nuclear program "is unclear," suggesting it could be more advanced than originally thought.

Outside experts, such as Pakistani nuclear engineer Bashir al-Din Mahmood, may have provided assistance to the group in advancing its nuclear program.

Bashir reportedly met with bin Laden and discussed nuclear weapons with him, the CIA said.

US intelligence officials have repeatedly assured they are trying to stay on top of the weapons proliferation threat.

But they also have complained the task is becoming increasingly complex and frustrating as the information age makes technical information increasingly available.

"Nuclear fuel-cycle and weapons-related technologies have spread to the point that, from a technical view, additional states may be able to produce sufficient fissile material and to develop the capability to weaponize it," the CIA said.

It warned that many developing countries advanced toward "at least latent chemical warfare capability" when they expanded their chemical industries into pesticide production.

The agency reiterated its concern that Iran was trying to develop a full nuclear fuel cycle that it intended to use for weapons production at covert facilities unknown to International Atomic Energy Agency inspectors.

But the unclassified version of its report said nothing about alleged clandestine work by Tehran to adopt its existing ballistic missile for a nuclear payload.

The document vaguely mentioned Iran's publicly acknowledged efforts to develop "follow-on versions" of the Shahab-3, its medium-range ballistic missile. However, it stopped short of saying how the missile was being modified.

On North Korea, the CIA said it was continuing to monitor Pyongyang's nuclear weapons program, but this time, offered no assessment of how many warheads the hermit nation might actually possess.

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