This week's threats by terror organization Al-Qaeda and three confirmed cases of anthrax in the U.S. state of Florida have stoked fears of another round of terrorist attacks. How credible are the threats and Al-Qaeda's claims that "thousands of young people" are willing to die in attacks like those of 11 September?
Prague, 11 October 2001 (RFE/RL) -- Since hijackers slammed passenger jets into key buildings in the United States last month, the country has been on edge, bracing itself for another potential terrorist attack.
There are signs of frayed nerves all over the U.S. as well as in other countries feeling at risk of an attack. Sales of guns and gas masks are up. Planes have been diverted after security alerts. And incidents which would have seemed relatively harmless before 11 September are now eliciting tough police responses.
For a nation already gripped by fear of more terrorist attacks, that anxiety has been cranked up an extra notch in recent days.
In the state of Florida, the authorities launched a criminal investigation on 10 October after one man died of anthrax poisoning and two of his colleagues were reportedly exposed to the deadly bacteria.
There's no word yet on whether the outbreak is terrorist-related. But the fact that three cases of an extremely rare form of the disease have occurred at this time strikes many people as too much of a coincidence.
On 9 October, the terrorist organization Al-Qaeda issued a threat to the U.S. that more attacks are in store. Al-Qaeda is headed by Osama bin Laden, the man the U.S. believes masterminded the 11 September attacks.
Al-Qaeda spokesman Sulaiman Bu-Ghaith said that "America must know that the storm of airplanes will not stop." There are thousands of young people, he said, who look forward to death like the Americans look forward to living.
The U.S. administration seems to be taking the threat seriously, with law-enforcement agencies reportedly focusing on trying to prevent a second round of attacks rather than investigating those of 11 September.
Intelligence officials are reported to have briefed members of Congress last week that there is a "100 percent chance" of further terrorist strikes against the U.S.
So how credible are these threats, and the claims that thousands of young people are willing to die in attacks like those of 11 September?
Paul Wilkinson heads the Center for the Study of Terrorism and Political Violence at St. Andrews in the U.K. He says we should take the threat seriously, even if the numbers of Al-Qaeda followers -- believed to be present in more than two dozen countries -- are disputable.
"I don't think we can possibly know how many they have recruited for this sort of task, but it would be foolish to ignore the characteristic of this organization, which is to use people in this way and to claim that in the course of what they regard as a holy war their followers should be prepared to sacrifice their lives. Even if that number mentioned by the spokesman is a huge exaggeration, even a small number -- as we've seen from the atrocities on 11 September -- can create huge carnage through suicide hijackings against heavily populated areas."
That's why Wilkinson says it's important to tighten security in the air, seal off cockpits -- like Israel's El Al airline has done for a number of years -- and put armed sky marshals aboard planes.
And he says people should be prepared for all kinds of terrorist tactics and not assume that the next one will take the same form.
"However, the degree of destruction and loss of life that can be caused by an airliner being used as a kind of flying bomb in a densely populated area is so dangerous that we should certainly give priority to measures to try to prevent that form of attack."
The other possible methods of attack make a spine-chilling list.
"The suicide truck bomb, the kind that was used in the  East African embassy bombings; the attack on ships, the kind of attack that was done by the bin Laden network on Aden harbor that caused the death of 17 U.S. sailors -- these are forms of attack which would clearly be attractive to the bin Laden leadership. And we also have to consider the possibilities of assassination attempts, the possibility of hostage-taking, the whole range of traditional terrorist methods."
In addition, he says it would be wise for governments to stockpile vaccines for anthrax and smallpox and step up vigilance to identify any groups attempting to acquire such biological material or recruit qualified people to help train them in its use.
Michael Clarke is the director of the Centre for Defence Studies at King's College in London. He also believes the Al-Qaeda threat is genuine, but adds that as a result of the investigations after 11 September, the bin Laden network in Europe and the U.S. has been fairly heavily penetrated.
"It's also fairly unlikely that one could number the 'sleeping' potential suicide terrorists in thousands. It's much more likely that we're looking at a few dozens of people, because most of what we know about international terrorist organizations in the past suggests that if you can get a few dozens of people into place, that in itself takes years and those people aren't always willing after 3 or 4 years living in a country to do the things they said they would do when they were in their training camps. So it seems to me that the threat has to be taken seriously, but the antiterrorist measures being enacted in the Western world will do quite a lot to militate against big attacks."
He says a series of smaller attacks is more likely than what he calls 11 September-style "spectaculars." These could be committed by Al-Qaeda or individuals or organizations acting in bin Laden's name.
These are more likely to employ traditional methods, as there's now no time to plan huge operations.
"Also, remember that the bin Laden networks are now on the back foot, they're on the run. It's very difficult to plan when they're on the run and one of the objectives of the present military campaign in Afghanistan is to make it very uncomfortable for the networks so that they can't plan 'spectaculars.' It seems to me what the more realistic threat now is of smaller, more conventional terrorist attacks that have high propaganda value, are very visual, things which are immediately apparent in television pictures. That's a very credible threat and I think that's a more likely outcome than a terrorist spectacular."
As for the likelihood of bio-terrorism, both Clarke and Wilkinson say it's harder than many people think to disperse germs in such a way that inflicts substantial damage. But it shouldn't be ruled out either, especially given intelligence information that suggests bid Laden's networks have access to some form of biological material.
Clarke says: "There's also the fact that chemical attacks have far less visual impact than aircraft, than something that actually explodes. And if people are suffering the effects of anthrax, say, there are things you can do about it. You can minimize the attack, you can close down water supplies. The state has ways of insulating the problem, whereas its has very little way of insulating the problem of a hijacked airliner flying into a building. Biological and chemical [attacks] are a credible threat, we should take it seriously, but we shouldn't be alarmist about this."
Clarke also says the small number of victims involved in the Florida anthrax case suggests it was not a terrorist attack.