A weapon of mass destruction will likely be used in a terrorist attack somewhere in the world by the end of 2013, a new U.S. government report suggests.

The 161-page document, titled World at Risk, also predicts that the weapon is more likely to be a biological rather than a nuclear weapon.

"Terrorists are determined to attack us again — with weapons of mass destruction if they can," says the report by a U.S. congressional commission.

After conducting about 250 interviews with experts, the commission concluded that "America's margin of safety is shrinking, not growing.

While the U.S. has focused its attention on nuclear weapons — taking such actions as securing stocks of fissile materials before terrorists can acquire enough to build a nuclear bomb — it has done little to prevent bioterrorism, the report says.

"As a result, security awareness has grown slowly, lagging behind the emergence of biological risks and threats," the report said.

Awareness of the problem posed by biotechnology is low compared to nuclear power. The commission attributes this in part to a lack of an iconic event in the life sciences field like that of the mushroom cloud for the nuclear age.

"At the same time that it has benefited humanity by enabling advances in medicine and in agriculture, it has also increased the availability of pathogens and technologies that can be used for sinister purposes."

The report recommends increasing security awareness among those working at universities, medical and veterinary schools, non-governmental research institutes and pharmaceutical companies.

The U.S. should conduct a review to secure dangerous pathogens and tighten oversight of high-containment laboratories, it says.

The report notes that it's hard to detect sinister biological activities since they can be used for "good as well as harm."

The report says the world has witnessed a "new era of proliferation" since the end of the Cold War — with North Korea testing a nuclear weapon, Iran developing its capabilities to build them and nuclear arms rivalries intensifying in the Middle East and Asia.

It also recommends that the U.S. move with "urgency" to stop proliferation of nuclear weapons nations.

According to the report, the number of states armed with nuclear weapons or seeking to develop them is increasing.