The World Health Organisation has warned governments to be alert to the risk of chemical or biological attacks.
The organisation called on governments to speed up their preparations for possible germ warfare attacks in the wake of the terror attacks on the US.
America has already grounded crop–dusting planes over fears they could be used by terrorists to spread chemical or biological agents.
WHO has released a draft report of its technical guide, Health Aspects of Biological and Chemical Weapons, to health ministries around the world earlier than planned.
The report was due to be released later in the year.
The organisation's executive director Dr David Nabarro told BBC Radio Five Live: "We hope that we are not being alarmist.
"Several countries have contacted the WHO over the last few days just wanting to reassure themselves about the kind of precautions they need to take in case there was any kind of deliberate use of biological agents.
"We think it is prudent to respond to make sure they get the information they need to plan in case such a terrible thing was to happen."
WHO continuously monitors possible disease outbreaks through its Global Outbreak Alert and Response Network, which aims to keep the international community constantly alert to the threat of outbreaks and ready to respond.Reuse content