WASHINGTON ( CNN ) -- Terrorists are likely to use a weapon of mass destruction somewhere in the world in the next five years , a blue-ribbon panel assembled by Congress has concluded . Police watch over travelers at New York 's Grand Central Terminal before Thanksgiving . They are more likely to use a biological weapon than a nuclear one -- and the results could be devastating , the chairman of the commission told CNN . `` The consequences of a biological attack are almost beyond comprehension . It would be 9/11 times 10 or a hundred in terms of the number of people who would be killed , '' former Sen. Bob Graham said . He cited the flu virus that killed millions of people in 1918 as an example . `` Today it is still in the laboratory , but if it should get out and into the hands of scientists who knew how to use it for a violent purpose , we could have multiple times the 40 million people who were killed 100 years ago , '' he said . Watch how officials worry about a biological terror attack » . The U.S. government `` needs to move more aggressively to limit '' the spread of biological weapons , the commission said in its report . Graham warned that such measures would be costly , but were necessary . `` The leadership of this country and the world will have to decide how much of a priority ... they place on avoiding the worst weapons in the world getting in the hands of the worst people in the world , '' he said . `` It is not going to be cheap . It is not going to be accomplished without some sacrifices . It wo n't be accomplished without putting this issue ahead of some other competing national and international goals . But I think our safety and security depend upon doing so , '' he added . Graham said a biological attack was more likely than a nuclear one because it would be easier to carry out . Biological weapons `` are more available , '' he said . `` Anthrax is a natural product of dead animals . Other serious pathogens are available in equally accessible forms . '' `` There are so many scientists who have the skills to convert a pathogen from benign , helpful purposes into an illicit , very harmful weapon , '' he added . But the commission warned that there is also a threat of nuclear terrorism , both because more countries are developing nuclear weapons and because some existing nuclear powers are expanding their arsenals . `` Terrorist organizations are intent on acquiring nuclear weapons , '' said the report , which was published Tuesday on the Internet and will be officially released Wednesday . CNN obtained a copy of the report Monday evening . It cited testimony before the commission from former Sen. Sam Nunn , who said that the `` risk of a nuclear weapon being used today is growing , not receding . '' The report recommends a range of measures , including increased security and awareness at biological research labs and strengthening international treaties against the spread of biological and nuclear weapons . `` Many biological pathogens and nuclear materials around the world are poorly secured -- and thus vulnerable to theft by those who would put these materials to harmful use , or would sell them on the black market to potential terrorists , '' the report warned . The commission expressed particular concern about the nuclear programs of Iran and North Korea , and about Pakistan , which it described as `` the intersection of nuclear weapons and terrorism . '' While observing that Pakistan is a U.S. ally , the report said , `` the next terrorist attack against the United States is likely to originate from within the Federally Administered Tribal Areas '' in Pakistan . The tribal areas lie in northwest Pakistan where the government exerts little control ; the United States says it is a haven for militants from both Pakistan and neighboring Afghanistan . Congress created the commission to investigate and report on WMD and terrorism in line with a recommendation from the 9/11 Commission , which compiled a report on the September 11 , 2001 , terrorist attacks on the United States . Commissioners heard testimony from more than 250 experts from around the world over the course of their six-month investigation . CNN 's Jeanne Meserve contributed to this report .
NEW : Next terror attack on U.S. likely to originate in Pakistan tribal areas , report says . Terrorists with biological weapons could kill millions , panel 's chairman says . Biological attack more likely than nuclear attack , report says . Number of nations with nuclear weapons also growing , panel says .