The fresh attempts to prove that it was a chemical weapons plant, from an intelligence briefing by the US on Monday, suggest America feels it has to make more of an effort to explain why it chose to hit the factory.
Sudan says the plant was just a pharmaceutical factory and has invited the international community to verify this. Critics of the US have said if the plant were a chemical weapons factory, then it would have released lethal material after the missile attack.
Washington has responded by saying the plant manufactured a precursor chemical, not VX gas itself. Nor would it be possible for untrained observers to see if the plant had been making this chemical,which would have taken up only a small part of the complex, US officials claim.
They say they had found traces of a key precursor chemical in soil samples from the factory. The chemical - O-ethyl methyl-phosphonothioic acid, or EMPTA - cannot be used for anything apart from the V-series nerve gases, the US claims.
"It is a substance that has no commercial applications, it doesn't occur naturally in the environment, it's not a by-product of any other chemical process. The only thing you can use it for, that we know of, is to make VX," a US intelligence official said.
However, the official would not say how the sample was obtained.
Chemical weapons experts believe the evidence presented so far is not strong enough. They point out that key components of chemical weapons have "dual use" and are also used in medicines, even bubble bath and shampoo.
Alfred Frey, a chemical weapons expert working for the United Nations, said yesterday that the name given was not conclusive scientific evidence that the plant was contributing to nerve gas production. "It could be a sign of degradation of VX, but this would not be sufficient," he said.
Mr Frey, a scientist with AC Labor, a Swiss laboratory that is currently examining parts of an Iraqi missile warhead for traces of the deadly nerve gas, added: "That would tell me I found this product [the compound] and no more."
Mr Frey, a weapons inspector in Iraq, said: "Of course it raises questions."
Beyond some anti-cancer drugs, he believes that few pharmaceutical products use phosphorus compounds.
Several phosphorus compounds are listed as "dual use" chemicals under schedule two and three of the 1993 Chemical Weapons Convention. Of its 168 signatories, 114 countries have ratified the ban on the production, use and stockpiling of chemical weapons. Sudan has not joined the convention, nor have Libya, Iraq and North Korea. All are regarded as high-risk countries by disarmament experts.
America also says the plant had links to Iraq. One of Iraq's leading chemical weapons experts, Emad al-Ani, had "close ties" with senior Sudanese officials at the factory, and with other plants around Khartoum.
The US has said that it learnt of these ties from intercepts of conversations between the plant and Iraqis and other Sudanese. Previous reports have indicated that the main centre for electronic intelligence gathering in the region was the US embassy in Nairobi, Kenya - which was itself the target of a car bomb, triggering the strikes on Sudan and Afghanistan.
The telephone intercepts also showed continuing links both to Osama bin Laden,whom Americans accuse of a campaign against the US, and to military officials in Khartoum, the US says.
Mr bin Laden twice ordered assassination plots against President Bill Clinton, US newspapers reported yesterday. The reports, attributed to US intelligence and security sources, appear linked to the proceedings of a New York grand jury, which spent about a year examining the case against Mr bin Laden, and resulted in a sealed indictment against the former Saudi Arabian.
The first assassination attempt was due to take place when Mr Clinton visited the Philippines in November 1994, New York newspapers reported. It was aborted because of the security surrounding the President's visit.
Ramzi Yousef - later convicted of the 1993 World Trade Center bombing - was the intended hitman. A second attempt was to have been made during the President's intended visit to Pakistan in February this year. The visit was cancelled. Yousef admitted to the Philippines attempt when he was arrested in 1995 in Pakistan. But the link to Mr bin Laden was provided by Wali Khan Amin Shah, one of his aides, the newspapers said.
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