Pakistan’s nuclear arsenal now totals more than 100 deployed weapons, a doubling of its stockpile over the past several years in one of the world’s most unstable regions, according to estimates by nongovernment analysts.

The Pakistanis have significantly accelerated productionof uranium and plutonium for bombs and developed new weapons to deliver them. After years of approximate weapons parity, experts said, Pakistan has now edged ahead of India, its nuclear-armed rival.

An escalation of the arms race in South Asia poses a dilemmafor the Obama administration, which has worked to improve its economic, political and defense ties with India while seeking to deepen its relationship with Pakistan as a crucial component of its Afghanistan war strategy.