The head of the World Health Organization (WHO) has urged governments to prepare for possible biological or chemical attacks by militant groups following the attacks on the US.
"We must prepare for the possibility that people are deliberately harmed with biological or chemical agents," Dr Gro Harlem Brundtland told a meeting of western hemisphere health ministers.
Dr Brundtland said there was global capacity and experience to control serious disease outbreaks, but stressed the need to strengthen national contingency plans.
She said the WHO was ready to help should nations face such attacks.
"During the last week we have upgraded our procedures for helping countries respond to suspected incidents of deliberate infection," she told the directing council of the Pan-American Health Organization.
Dr Brundtland said guidelines for containing disease outbreaks were available on the WHO website.
Earlier, US Attorney General Mr John Ashcroft confirmed Mr Mohamed Atta, one of those suspected in the attacks, had been learning about crop-dusting aircraft to carry out a chemical attack.
He said the FBI feared such an attack was likely and that security officials nationwide were on alert to prevent it.
Any infectious agent or toxic chemical could in theory be engineered for deliberate use as a weapon. Experts believe smallpox, anthrax, botulism and plague are most likely to be used.
There are indications some countries, such as Iraq, have researched using them as weapons.