Weapons inspectors have been digging in the Iraqi desert for missing Iraqi Scud missile warheads, and tests of warhead fragments found at one site have, according to the inspectors, revealed evidence that Iraq filled at least some of them with the deadly gas.

These findings appear to be a blow to renewed hopes following the last Gulf crisis that quick progress can now be made on Iraqi disarmament. They could mean the inspectors have to make a major reassessment of Iraq's VX programme.

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A BBC correspondent in Baghdad says the new findings are likely to be hotly debated in the UN Security Council, where there are sharp divisions over how to deal with Iraq.

US officials say the discovery will strengthen their hand in maintaining tough economic sanctions on Iraq when the issue is taken up by the Security Council later this week.

State Department spokesman James Rubin said the report demonstrated "how important it is for sanctions to remain in place until Iraq cooperates with UNSCOM".

Unnamed UN sources quoted by the Associated Press news agency, said Richard Butler, chief of the UN inspection team, reported to the council last week that Iraq had been told about "the preliminary results of the chemical analysis of certain excavated remnants of special warheads.

"While informed of the commission's concerns, Iraq refused to undertake additional steps to clarify the extent of its attempts to produce the chemical warfare agent VX."

Iraq's admission

In Baghdad, Deputy Prime Minister Tariq Aziz said Iraqi scientists had experimented with VX but were unable to turn it into a weapon.

He said in a letter to the Security Council last week that 1.7 tons of the agent had been produced but was not of weapons grade.

According to the Washington Post, where the report originated, the information on the nerve gas is included in a confidential US Army laboratory analysis of warhead fragments taken from a pit at Taji, Iraq, in March.