Adding: Ukraine voluntarily surrendered the world's third largest nuclear weapons arsenal in exchange for these assurances.
The vessels carry a total of 160 nuclear warheads, making Britain the world's fifth largest nuclear power, after the United States, Russia, China and France.
Pakistan, which is now the fourth largest nuclear armed state in the world, has been gravely destabilized by its involvement in wars in Afghanistan.
"And judging by the new nuclear reactors that are coming online and the pace of production, Pakistan is on a course to be the fourth largest nuclear weapons state in the world, ahead of France," he said.
"If not now, Pakistan will soon have the fifth largest nuclear arsenal in the world, surpassing the United Kingdom," said Bruce Riedel, a former C.I.A. officer and the author of "Deadly Embrace: Pakistan, America, and the Future of Global Jihad".
But throughout this period, Ukrainians had not been aware of the size of the nuclear arsenal on their soil Ukraine was effectively the third largest nuclear power in the world at the time nor had they considered the high costs and logistical problems of nuclear divestment.
WASHINGTON — New American intelligence assessments have concluded that Pakistan has steadily expanded its nuclear arsenal since President Obama came to office, and that it is building the capability to surge ahead in the production of nuclear-weapons material, putting it on a path to overtake Britain as the world's fifth largest nuclear weapons power.
Soon after independence, Mr. Nazarbayev declared that he would rid his country of what would have been the world's fourth largest nuclear arsenal and the numerous chemical and biological weapons facilities with which, he said, the Soviet Union had "stuffed" his country.
Pakistan is also the world's fifth largest nuclear power, according to recent reports.
