Drawn from the US Army's special mission units known as Delta Force, Task Force 20 "found no working nonconventional munitions, long-range missiles or missile parts, bulk stores of chemical or biological warfare agents or enrichment technology for the core of a nuclear weapon," said the daily.

Citing sources with firsthand knowledge of the unit's mission and others with access to its reports, the post said Task Force 20's sent "a stream of "initiallly promisint reports" to a small group of Washington officials.

Those reports prompted US President George W. Bush and his senior national security advisers to feel optimistic about the eventual discovery of illegal weapons in Iraq, the military and intelligence sources in Washington and Baghdad told the daily.

Britain and the United States have come under increasing pressure to account for the lack of any proof of WMDs found so far in Iraq, before or after the coalition war in March and April that removed Saddam Hussein from power.

A proposed investigation by the US Senate into the apparent discrepancy between pre-war US intelligence reports on Iraq's weapons programs -- which motivated the war on Iraq -- and the post-war reality was rejected earlier this week by the Republican majority in the upper house -- Bush is a Republican.

Task Force 20's chief assignment is to "seize, destroy, render safe, capture, or recover weapons of mass destruction," according to a Special Operations mission statement obtained by The Washington Post.

In what is described as "far more important than that of the search teams operating in the open," the task force "staged raids ahead of the US and British ground advance to seize suspected caches of nonconventional arms, gathered hundreds of weapons samples and captured as many as half of the 'high value' weapons scientists and Baath Party leaders now in US custody, the daily said.

So far, military and intelligence sources told the daily, "the expectations are unfulfilled."

The army unit is admired for its exploits, the sources told the daily. Among other missions, it was responsible for rescuing US army prisoner of war Jessica Lynch, captured Palestinian guerrilla leader Mohammed Abbas in Baghdad in mid April and the Iraqi scientists nicknamed Mrs. Anthrax and Dr. Germ.

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