(Reuters) - An assault on a naval base in Karachi is the latest militant attack on military installations in Pakistan, raising fears about the safety of the country's nuclear arsenal.

Pakistan has the fastest growing nuclear arsenal in the world and in a decade could pass France as the fourth-largest nuclear power, so such brazen attacks on secure military establishments -- militants also attacked the General Headquarters in Rawalpindi in 2009 -- give Western leaders nightmares about militants acquiring nuclear materials, or worse, an entire weapon.