The review, ordered by the National Intelligence Council, was expected to produce two major papers -- a new National Intelligence Estimate (NIE) on Iran and a so-called "memo to holders," the officials said.

"It involves the entire intelligence community to write these products," said one of the officials, who spoke to AFP on condition of anonymity.

The official gave no specific date but said the new NIE was "coming out" while the memorandum was expected "several months from now."

The official made a point to say that the "memo to holders" was "self-initiated." "It is not that somebody has requested it," the official added.

The United States relied extensively on a similar intelligence review in arguing its case to go to war on Iraq in 2003, but the intelligence community has not produced a formal estimate on Iran since 2001.

Analysts said the new focus on the country likely reflected new strategic priorities for the administration of President George W. Bush, who has accused Iran of "pursuing nuclear weapons while depriving its people of the freedom they seek and deserve."

A report in The Washington Post Sunday meanwhile revealed that the United States has been flying drones over Iran since April 2004, seeking evidence of nuclear weapons programs and probing for weaknesses in Iran's air defenses.

Such aerial espionage is standard in military preparations for an eventual air attack and is also employed as a tool for intimidation, the Post pointed out.

Officials familiar with the program told the daily the surveillance had thus far added little new information about Iran's nuclear activities.

The CIA-led intelligence review was expected to parallel a reassessment of information about Iran being undertaken by the Senate intelligence committee, which was to hold a series of closed-door hearings on the matter in coming months, according to congressional officials.

Last year, the committee probed the US failure to find weapons of mass destruction in Iraq, whose alleged presence in the country served as the prime rationale for the March 2003 invasion.

A scathing report produced as a result of this investigation accused the intelligence community of "group think," "poor management" and "inadequate intelligence collection."

The Central Intelligence Agency told Congress late last year that Iranian efforts to develop an indigenous nuclear fuel cycle had "clear weapons potential."

In its most recent report on proliferation matters, the CIA suggested International Atomic Energy Agency inspections and safeguards will most likely prevent Tehran from using its declared nuclear facilities for its weapons program as long as Tehran remains a party to the nuclear Non-Proliferation Treaty.

"However, Iran could use the same technology at other, covert locations for military applications," the agency warned.

Moreover, the CIA said that Iran "may have already stockpiled" various types of deadly chemical agents and "probably has the capability to produce at least small quantities" of biological weapons.

The intelligence reviews come as rhetoric surrounding Iran's suspected nuclear weapons drive is heating up, with US Vice President Richard Cheney pointing out last week that while the United States preferred a diplomatic solution, "we have not eliminated any alternative."

Iranian President Mohammad Khatami, for his part, warned on Thursday that anyone who will try to invade Iran would be greeted with a "burning hell."

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