Pakistan, which has kept open the option of first use of atomic weapons against 'nuclear-armed aggressors', has also developed a second strike capability, a Congressional report has said.
"Pakistan has reportedly addressed issues of survivability through second strike capability, possible hard and deeply buried storage and launch facilities, road-mobile missiles, air defenses around strategic sites and concealment measures," the Congressional Research Service (CRS) said in its report on Pak nuclear weapons dating May 15.
CRS is the research wing of US Congress, which prepares reports on issues of interest of the US lawmakers.
Pakistan has also pledged 'no-first-use' against non-nuclear-weapon states, but has not ruled out first-use against a nuclear-armed aggressor that attacks Pakistan - for instance, India.
Islamabad has time and again said that its nuclear weapons are targeted primarily towards India and are aimed to act as a deterrent against a larger neighbour.
"Analysts say this ambiguity serves to maintain deterrence against India's conventional superiority. Others argue that keeping the first-use option against New Delhi allows Islamabad to conduct sub-conventional operations, such as support for low intensity conflict or proxy war in Kashmir, while effectively deterring India at the strategic level," the CRS said.