LONDON, March 24 (Xinhua) -- The threat of an attack on Britain involving chemical or nuclear weapons is now "more realistic," a senior government official warned Tuesday.

    Home Secretary Jacqui Smith highlighted the danger posed by new technologies and failed states around the world as she published an updated counter-terror strategy, Sky News said.

    The report, "Contest Two," is the first public document to contain a detailed assessment of the underlying causes of the terrorist threat and its likely future direction.

    The report said "contemporary terrorist organizations aspire to use chemical, biological, radiological and even nuclear weapons.

    "Changing technology and the theft and smuggling of chemical, biological, radiological and nuclear and explosive materials make this aspiration more realistic than it may have been in the recent past," Smith was quoted by Sky News as saying.

    The report also notes that terrorists have created new explosives and new ways of using them, and that technology developed in conflict zones is quickly shared around the world.

    The report said the threat to Britain came primarily from four sources: the al Qaeda leadership, terrorist groups affiliated withal Qaeda, "self-starting" terror networks or lone individuals motivated by an al Qaeda-style ideology, and terrorist groups with a similar ideology to al Qaeda.

    The document said al Qaeda itself was "likely to fragment" under international pressure, and might not survive in its current form.

    But its ideology will outlive changes to its structure, possibly leading to greater threats to Britain from smaller "self-starting" organizations.

    The Contest strategy is divided into four strands -- Prevent, Pursue, Protect and Prepare.

    These cover preventing the radicalization of potential terror recruits, disrupting terror operations, reducing the vulnerability of Britain and ensuring the country is ready for the consequences of any attack.

    Smith called for the use of "civil challenge" to those who hold extremist viewpoints.

    She cited the example of the Muslim activists who recently protested at a homecoming parade in Luton for British forces returning from Iraq.

    "The civil challenge means that, if people feel it appropriate to demonstrate against our troops coming home from defending this country abroad, we -- as government and others -- will say in turn that we think that that's wrong," she said.