As it accuses Iran of trying to develop nuclear weapons, America is preparing to upgrade and renew parts of its own ageing nuclear arsenal. Critics believe the upgrades could lead the US to breach the treaty banning the testing of nuclear weapons.

Since the project will probably involve replacing technology that originated in the Sixties, watchdogs are concerned the US might be inclined to test the newer systems and, therefore, breach the 1996 Comprehensive Test Ban Treaty.

Of more concern to watchdogs is President George Bush's dedication to developing a new breed of "bunker-buster" nuclear weapon, designed to penetrate toughened underground defences. Critics say the plan reveals the administration's hypocrisy and undermines international efforts to persuade other countries not to develop weapons..