Nearly 380 tonnes of deadly explosives, powerful enough to shatter air planes, demolish buildings, make missile warheads and detonate nuclear weapons, are missing from one of Iraq's most sensitive former military installations, the interim government has warned the US and international nuclear inspectors.

The huge facility, called Al Qaqaa, was supposed to be under American military control but is now a no man's land, still picked over by looters as recently as Sunday.

American weapons experts said their immediate concern was that the explosives could be used in bombing attacks against American or Iraqi forces. The explosives, mainly HMX and RDX, could produce bombs strong enough to shatter aircraft or tear apart buildings, the New York Times reported.

United Nations weapons inspectors had monitored the explosives for many years, but White House and Pentagon officials acknowledge the explosives vanished some time after the American-led invasion in 2003, the report said.

The White House said President George W Bush's National Security Adviser Condoleezza Rice was informed within the past month that the explosives were missing. It is unclear whether President Bush was informed.

American officials have never publicly announced the disappearance, but beginning last week they answered questions about it posed by the Times and the CBS News programme 60 Minutes.

The Times quoted administration officials as saying on Sunday that the Iraq Survey Group, the Central Intelligence Agency task force that searched for unconventional weapons, has been ordered to investigate the disappearance of the explosives.

A senior military official noted that HMX and RDX were 'available around the world' and were not on the nuclear nonproliferation list even though they are used in the nuclear warheads of many nations.

The bomb that brought down Pan Am flight 103 over Lockerbie, Scotland, in 1988 used less than a pound of the same type of material, and larger amounts were apparently used in the bombing of a housing complex in November 2003 in Riyadh, Saudi Arabia, and the blasts in a Moscow apartment complex in September 1999 that killed nearly 300 people, the Times said.

The explosives could also be used to trigger a nuclear weapon, which was why international nuclear inspectors had kept a watch on the material, and even sealed and locked some of it. The other components of an atom bomb - the design and the radioactive fuel - are more difficult to obtain, the paper said.

"This is a high explosives risk, but not necessarily a proliferation risk," one senior Bush administration official told the Times.

The International Atomic Energy Agency (IAEA) publicly warned about the danger of these explosives before the war, and after the invasion it specifically told US officials about the need to keep the explosives secured, European diplomats told the Times in interviews last week.

US officials told the daily they couldn't explain why the explosives were not safeguarded, beyond the fact that the occupation force was overwhelmed by the amount of munitions they found throughout the country.

A Pentagon spokesman, Lawrence Di Rita, said on Sunday that Saddam Hussein's government 'stored weapons in mosques, schools, hospitals and countless other locations' and that the allied forces 'have discovered and destroyed perhaps thousands of tonnes of ordnance of all types'.

The Qaqaa facility, about 45km south of Baghdad, was well known to American intelligence officials: Hussein made conventional warheads at the site and the IAEA dismantled parts of his nuclear programme there in the early 1990s after the 1991 Gulf War.

In the prelude to the 2003 invasion, Bush cited a number of other 'dual use' items, including tubes that the administration contended could be converted for use in the nuclear programme, as justification for invading Iraq, the Times noted.

After the invasion, when widespread looting began in Iraq, the international weapons experts grew concerned that the Qaqaa stockpile could fall into unfriendly hands.