The decision to close down the national nuclear security administration advisory committee - required by law to hold public hearings and issue public reports on nuclear weapons issues - has come just days before a closed-door meeting at a US air force base in Nebraska to discuss the development of a new generation of tactical "mini nukes" and "bunker buster" bombs, as well as an eventual resumption of nuclear testing.

Ed Markey, a Democratic congressman and co-chairman of a congressional taskforce on non-proliferation, said: "Instead of seeking balanced expert advice and analysis about this important topic, the department of energy has disbanded the one forum for honest, unbiased external review of its nuclear weapons policies."

An NNSA spokesman, Bryan Wilkes said: "The advisory committee was created to assist the NNSA administrator during the creation of the NNSA, and it was not intended to go on beyond two years. Clearly the NNSA is up and running and it is not needed any more."

The typical lifetime of such federal advisory committees is two years. However the NNSA committee's charter stipulates "The Committee is expected to be needed on a continuing basis."

Former members of the advisory committee said they had the impression that the new administrator, Linton Brooks, appointed last year, was not interested in its work, and decided not to renew its charter.

Sidney Drell, a leading American physicist and a former committee member said: "It was not renewed. I presume they did not value us or found us a nuisance. An independent, tough advisory board is very important in having a strong (nuclear) stockpile programme."

The committee's charter said that it's meetings "will be held approximately four times each year". In fact, it was not summoned at all in the last year of its existence.

"They just didn't call us. We didn't hear from them," Prof Drell said.

Prof Drell and Raymond Jeanloz, a planetary science professor at the University of California at Berkely, co-authored an article earlier this year that was highly critical of the plans for new weapons.

"Rather than moving to develop new nuclear weapons, the United States should push to strengthen the nonproliferation regime through example and through stronger compliance measures directed at those who flout its basic purposes," they wrote in the March 2003 edition of Arms Control Today, a few months before the panel was disbanded.

The statute establishing federal advisory committees requires their dissolution to be officially gazetted in the federal register but in the end, the NNSA panel was abandoned quietly, by a simple email to its members.

Daryl Kimball, the head of the independent, Washington-based Arms Control Association, said: "This will make the department of energy and the NNSA even more opaque. It will be all the more difficult to understand what they are planning to do."

Hawks in the Pentagon and the energy department are pushing for the development of tactical nuclear weapons with yields of less than 5 kilotons and hardened "bunker buster" nuclear bombs, designed to penetrate deeply buried targets, where enemy leaders or weaponsmay be hidden.

According to the leaked agenda for the Omaha meeting in early August, Pentagon and energy department officials will discuss how to test small numbers of these new weapons, and whether this will require a break from the moratorium on nuclear tests.

Critics argue that the new weapons will blur the distinction between conventional and nuclear arms, and trigger a new arms race.