WASHINGTON, Feb 14: Use of stolen or purchased nuclear weapons from Pakistan or Russia by terrorists cannot be ruled out within the next 15 years, says the latest CIA report.

Prepared by the prestigious nerve centre of strategic thinking in the US intelligence community, the National Intelligence Council, the report says that most terrorist attacks will continue to employ primarily conventional weapons, incorporating new twists to keep counter terrorist planners off balance.

The 119-page report, issued every five years, warns that terrorists probably will be most original not in the technologies or weapons they employ but rather in their operational concepts.

One such concept that is likely to continue is a large number of simultaneous attacks, possibly in widely separated locations. While vehicle-borne improvised explosive devices will remain popular as asymmetric weapons, terrorists are likely to move up the technology ladder to employ advanced explosives and unmanned aerial vehicles, the report says.

The religious zeal of terrorists increases their desire to perpetrate attacks resulting in high casualties. "Historically, religiously inspired terrorism has been most destructive because such groups are bound by few constraints," the NIC warns.

"The most worrisome trend," according to this report, has been an intensified search by some terrorist groups to obtain weapons of mass destruction. The "greatest concern" of the US intelligence community, is that these groups might acquire biological agents or a nuclear device.

The report says that the possibility of terrorists using biological agents is stronger, and the range of their options will grow. "With advances in the design of simplified nuclear weapons, terrorists will continue to seek to acquire fissile material in order to construct a nuclear weapon," the NIC report says.

This could encourage countries without nuclear weapons, especially in the Middle East and Northeast Asia, to seek them as it becomes clear that their neighbours and regional rivals already are doing so.

"The assistance of proliferators, including former private entrepreneurs such as the A. Q. Khan network, will reduce the time required for additional countries to develop nuclear weapons.

"Concurrently, they can be expected to continue attempting to purchase or steal a weapon, particularly in Russia or Pakistan. Given the possibility that terrorists could acquire nuclear weapons, the use of such weapons by extremists before 2020 cannot be ruled out.

We expect that terrorists also will try to acquire and develop the capabilities to conduct cyber attacks to cause physical damage to computer systems and to disrupt critical information networks.